The path to the mountain gorillas is not for the fainthearted. For nearly two hours here in Congo, I have climbed almost vertically up a rocky trail through dense jungle, ever wary of running into the anti-government rebel militias that swarm through these mountains. Leading the way are two trackers and three armed rangers who, charged with ensuring the safety of the four gorilla families that live on these slopes, make this journey routinely.

At some 10,000 feet above sea level, on the slopes of Mount Mikeno, a dormant volcano in the Virunga Mountains, the trackers pick up signs of a gorilla clan led by a silverback—so-called for the distinctive silver saddle that appears on a mature male's back—named Humba. The men hack a path through walls of creepers, bamboo and prickly vines, following a trail left by the gorillas. Suddenly, the lead tracker holds up a hand to halt us. He utters a few hoarse coughs—gorilla-speak to tell the great apes we come in peace.

Moments later, about ten yards ahead, Humba yanks aside the creepers to stare at us with imperious grace. His muscled body ripples with power, and his massive head has the gravitas of a Mount Rushmore president. He bares his fearsome canine teeth. "Don't be afraid," a ranger whispers, "he's used to people."

It's the gorillas that have reason to fear. Only about 750 mountain gorillas are left in the world: 350 in Uganda, 270 in Rwanda and a mere 150 here in Congo (formerly Zaire). They have been ravaged by poaching, habitat loss, disease and the violence of war. Many live in lawless regions, sharing territory with armed rebels from Uganda or the remnants of Hutu militias responsible for Rwanda's 1994 genocide of ethnic Tutsis. Today the biggest threat comes from the Congolese area of their range. Rebel groups opposed to Congo president Joseph Kabila control territory in the turbulent east. The most powerful group is led by an ethnic Tutsi named Laurent Nkunda, who commands thousands of well-armed rebels in the Virungas. Not far from here in January, troops from Nkunda's group killed and presumably ate two silverbacks. A female was shot in May, another male and four females were slain in July; their killers had not been identified as we went to press.

It is the desperate plight of mountain gorillas that has brought me halfway across the world to see what is being done to protect them. For one hour (strictly enforced to minimize the animals' exposure to human disease), we watch the silverback and three adult females and five youngsters as they eat, play and doze in their perilous paradise. Every 10 or 15 minutes, Humba knuckle-walks farther up the slope in search of food, followed by his family. I stumble after them.

When our hour is up and we have begun winding our way back down the mountain, I hear voices and glimpse camouflage uniforms though gaps in the thick foliage. At one point, we come face to face with about 40 soldiers brandishing assault rifles, rocket-propelled grenades and machine guns. Bandoleers of bullets are strung across their chests. "They're Rwandan Army troops," says Emmanuel de Merode, executive director of WildlifeDirect, a Nairobi-based nonprofit organization that helps fund the rangers and trackers. "They've illegally crossed into the Congo, so don't take any pictures, or they'll probably shoot you."

My journey to the isolated mountain gorillas of eastern Congo began in Nairobi, Kenya, where I met Richard Leakey, 62, chairman of WildlifeDirect. In the 1950s and 1960s, Leakey's paleoanthropologist father, Louis, best known for his research on human origins in Africa, famously chose Dian Fossey, Jane Goodall and Biruté Galdikas to study our closest animal relatives: mountain gorillas, chimpanzees and orangutans, respectively. Richard's wife Meave and daughter Louise recently helped discover (with Fred Spoor, see "Interview") two fossils that change our understanding of the hominid family tree.

Richard Leakey is credited with saving Kenya's elephants. In 1989, as head of the Kenya Wildlife Service, he gained world attention when he set fire to 2,000 poached elephant tusks and ordered his rangers to shoot poachers on sight. Today Kenya has about 25,000 elephants, up from 16,000 in 1989. Leakey lost both legs in a light-plane crash and has received two kidney transplants. Undaunted, he has channeled his energy into building WildlifeDirect, which he created last September. The organization pays for park rangers' salaries and supplies. Until recently, the rangers went unpaid for years at a time. "Since the beginning of armed conflict in eastern Congo [a civil war started in 1994], over 150 rangers have been killed on active service," Leakey says. "Despite the minimal support, Congo's rangers risk their lives on a daily basis."

Since getting to the Congolese mountain gorillas is difficult and dangerous, Leakey assigned de Merode and Samantha Newport, another staff member, to meet me in Congo and help me reach the gorillas there.

My first stop is a short flight away, to the Rwandan capital, Kigali, where I stay overnight at the Hotel des Mille Collines, also known as the Hotel Rwanda. (The tall, modern building looks nothing like the two-story safari hotel in the movie of the same name, most of which was filmed in South Africa.) I sleep uneasily, thinking of the Tutsi families who may have occupied the room while the Hutu militia rampaged outside more than a decade ago. I decide not to take a dip in the swimming pool, which for a time was the Tutsi refugees' only source of drinking water.

The next day, en route to joining some tourists to visit Rwanda's mountain gorillas, I pass Kigali's prison, where an armed guard watches over about 30 men clad in prison-issue pajamas. "They're most likely Interahamwe [Those Who Act Together]," my driver says, referring to the Hutu militia who murdered most of the 800,000 to one million Tutsis and moderate Hutus—men, women and children—during three months in 1994, most of them by machete.

After a two-hour drive, we reach the town of Ruhengeri in the shadow of the Virunga Mountains, a chain of eight volcanoes that thrust up to 14,000 feet above sea level in a 50-mile arc. In 1861, British explorer John Speke was warned that the Virungas' slopes were inhabited by man-like monsters. But only in 1902 did a German officer, Capt. Oscar von Beringe, become the first European to report seeing mountain gorillas, on Mount Sabyinyo's slopes above Ruhengeri. He shot two of them, and the subspecies was named Gorilla beringei beringei. Over the next two decades, Western expeditions killed or captured 43 more. Five shot by American naturalist Carl Akeley in 1921 can be seen in a diorama at New York's American Museum of Natural History.

"As he lay at the base of the tree," Akeley wrote of one of his trophies, "it took all one's scientific ardor to keep from feeling like a murderer. He was a magnificent creature with the face of an amiable giant who would do no harm except perhaps in self-defense or in defense of his friends." To protect the animals, Akeley persuaded Belgium, the colonial power in what was then called Ruanda-Urundi, to create Albert National Park in 1925, Africa's first. It was renamed Virunga National Park in 1969.

Forty years ago, Dian Fossey fled a bloody civil war on the Congo side of the Virungas, where she had been studying mountain gorillas, to pitch a tent on the Rwandan side. She spent much of the next 18 years there with her beloved gorillas, until in 1985 she was murdered by an assailant, still unknown. Fossey's best-selling memoir, Gorillas in the Mist, and the movie based on it, demolished the belief that gorillas were man-killing beasts. It also sparked a multi-million-dollar boom in mountain gorilla tourism. Today visitors are largely confined to the Rwandan and Ugandan preserves because of danger from Congolese militias.

Shortly after dawn, at the headquarters of Volcanoes National Park on the outskirts of Ruhengeri, about 40 tourists, most of them American, gather for a trek to the seven mountain gorilla families on the Rwandan side. Each visitor pays $500 for a one-hour visit. Despite the cost, the park's chief warden, Justin Nyampeta Rurangirwa, tells me that there is a yearlong waiting list. The revenue is vital to Rwanda's feeble economy. "We earn about $8 million yearly from the entrance fees, and more millions from our visitors' hotel, travel and food costs," he says.

When I was last in Ruhengeri, a decade ago, reporting on the fate of mountain gorillas after the Rwandan genocide, the Interahamwe was using the gorilla habitat to move between Rwanda and what was then still called Zaire on raids. The Hutu militia also seeded the mountain passes with land mines to prevent pursuit by their enemies. Nyampeta Rurangirwa sighs at the memory. "Despite the fighting," he says, "only one mountain gorilla was killed on our side of the border. A silverback named Mrithi was shot dead because a soldier stumbled into him during a night patrol and thought he was a rebel."

Ten years ago, the militia were still terrorizing Ruhengeri and villages around it. A few months after I left, they murdered three Spanish aid workers and badly injured an American. Weeks later, they killed a Canadian priest. But Nyampeta Rurangirwa says that these days the town, and the gorillas on the Rwandan side of the border, are safe. Even poaching—a serious problem a decade ago—has been cut to a negligible level, at least in the national park. Rope and wire snares, used to capture small antelope but very dangerous to gorillas as well, are also less of a problem. "Our rangers patrol vigorously in the park, and that's a major reason they rarely come across snares nowadays," Nyampeta Rurangirwa tells me.

Mountain gorillas also benefit from the oversight of the Mountain Gorilla Veterinary Project (MGVP), a conservation program proposed by Fossey shortly before her death and now affiliated with the Maryland Zoo. When I came here the first time, the project employed just two veterinarians working out of a bungalow. Now it has a modern base equipped with a laboratory and more than 20 staff members across three countries, including six veterinarians.

The head vet is Lucy Spelman, the former director of the National Zoo in Washington, D.C. She climbs the slopes every couple of days to check on gorillas, looking for symptoms such as limping, coughing, hair loss and diarrhea. Because mountain gorillas are so closely related to humans, she tells me, they can catch such diseases as polio, measles, strep throat, tuberculosis and herpes from us, as well as salmonella and rabies from animals. If necessary, MGVP workers anesthetize gorillas with darts and then inject them with antibiotics to treat infections.

Spelman says that mountain gorillas in the Virunga region have increased by 17 percent since 1989, thanks in part to ranger patrols and the MGVP. "Ours is the first veterinary service to look after an endangered species in its natural environment," she says. She is raising a 4-year-old orphan, Maisha, who was seized from poachers. Only a few other mountain gorillas are in captivity (most gorillas in zoos are western lowland gorillas). Spelman hopes to return Maisha to the wild—a world first if she succeeds.

The border crossing from Rwanda to Congo is an hour's drive to the west, and getting to it is like descending from an earthly paradise into the outer gates of hell. Mount Nyiragongo erupted in January 2002, spewing molten lava down onto the Congo town of Goma. Half a million people fled as the eruption destroyed 80 percent of Goma's commercial district, smothering it with a blanket of lava up to 15 feet deep.

"Goma should not be rebuilt where it is now," Naples University volcanologist Dario Tedesco declared after inspecting the devastation a few days after the disaster. "The next eruption could be much closer to the town, or even inside it." Despite his warning, most of Goma's residents returned—they had nowhere else to go—only to be forced to flee again last December when warlord Nkunda threatened to occupy the town. A counterattack by U.N. peacekeeping forces based in Goma sent the rebels back into the jungles.

The 4,000 U.N. troops, most of them from India, are led by Brig. Gen. Pramod Behl. At his barricaded headquarters, he tells me that the region remains unstable and dangerous and that Nkunda's troops are "still raping and pillaging." He also alerts me to the presence of Mai Mai rebels, fierce Ugandan dissidents holding out along the Rwanda-Congo border, and some 5,000 Interahamwe, who are unwilling to return to Rwanda for fear of imprisonment or worse. Clearly, he adds, the gorillas "need all the help they can get."

Back in town, my eyes sting and my nose clogs from the volcanic dust thrown up by a brisk wind and aid workers' SUVs. Grim-faced Congolese police patrol the streets in single file; three men allegedly killed a priest and a carpenter the night before, and the police had to rescue the men from a mob. "The authorities put on this show of force for fear the smoldering resentment will flare into violence," says Robert Muir, who has lived in Goma for four years as a conservationist for the Frankfurt Zoological Society.

On Goma's outskirts, shantytowns give way to green fields on either side of a potholed road that is patrolled by hundreds of Congolese soldiers with assault rifles. We pass the vast muddy fields where a million Hutu refugees lived in tents for years after fleeing the Tutsi army. Almost all of them have returned to their villages, and only a few scattered tents remain.

At a turnoff, our four-wheel-drive van heads up a track studded with lava rock, and we bounce around like pinballs. The hills are dotted with mud-hut villages, whose volcanic fields flourish with crops, mostly potatoes and corn. Looming over this deceptively peaceful landscape is Mikeno, the 14,557-foot volcano on whose cloudy slopes live Humba and his family—as well as other Congo mountain gorillas.

Two hours later, we reach our destination, the Bukima patrol post, a dilapidated weatherboard hut that is home to the rangers who accompany the gorilla trackers each day. Jean Marie Serundori, the post's chief ranger, has spent 17 years with the gorillas. "So many of our rangers have been killed by rebels and poachers in the park," he tells me as Newport translates. "Two months ago, hundreds of Nkunda's troops occupied this very spot and looted it, remaining until just two weeks ago. We fled at the time, and have only just returned. [The rebels] are still just a few miles from here." I ask him why he risks his life by returning. "The gorillas are our brothers," he responds. "I know them as well as my own family. If we don't check that they're safe every day, soldiers and poachers might harm them." Rangers sometimes name newborn gorillas after community leaders who have recently died.

Serundori leads us through terraced fields where villagers are turning over the rich soil with hoes. Serundori says that a big silverback named Senkekwe—but better known as Rugendo—is nearby with his family, 12 members in all. "The gorillas like to raid the fields, especially to eat the corn."

As we enter the park, the dense canopy casts the jungle into verdant gloom. I struggle to breathe as we climb a steep, rocky slope. Minutes later, Serundori utters the rasping call that he says the gorillas interpret as "peace." He points at the thickets ahead. "Le grand chef, the big chief, is in there."

Within moments, we hear the thock, thock, thock of a silverback beating his barrel chest, a thrilling sound that echoes through the jungle. I tense as the six-foot-tall Rugendo, weighing probably 450 pounds, bustles through the thicket, then relax as he heads past us into the jungle. He is followed by a young, imp-faced male named Noel, so called, Serundori whispers, "because he was born on Christmas Eve three years ago." Rangers can tell one gorilla from another by the shape of their noses.

Another young male crashes through the branches, performs a perfect gymnast's roll and scurries after his gargantuan father. A potbellied mature female waddles past, barely glancing at us. Serundori leads me nearer to Rugendo, who sits by a cluster of small trees munching on fistfuls of leaves.

The mountain gorillas are swathed in the shaggy black fur that keeps them warm in their high-altitude habitat, between 7,300 and 14,000 feet above sea level. Mountain gorillas, a subspecies of eastern gorilla, are herbivores, apart from the occasional feast of ants. A silverback has to eat up to 75 pounds of vegetation a day to maintain his great bulk. Females, who weigh about half as much, leave their natal groups between ages 6 and 9 to search for a mate and bear their first offspring around age 10. Young males are called blackbacks. Once they begin to show silver, at about age 12, most leave or are forced out of the group, but some stay and wait for a chance at the dominant male's spot.

A dominant male will lead the group, usually around ten gorillas strong, for about ten years before being overthrown. Silverbacks are devoted fathers. If a mother dies or abandons her infant, the silverback will take over its raising, Serundori says, adding: "I've seen it many times." A silverback keeps his family under his watchful eye at all times. He wakes them about 5 a.m. by beating his chest and charging at them. Then he leads them to their first feeding spot for the day. "The family forages for about two miles a day, eating plants, leaves, wild celery, fruits and even thistles," says Serundori. "They play a lot, and take midmorning and midafternoon naps. Around 6 p.m. the silverback chooses a place for them to sleep for the night."

As if on cue, Rugendo rolls onto his side for a mid-afternoon nap, sated by his bulky snack. He became the master of this group in 2001, when his father was killed by crossfire between the Congolese military and the Interahamwe. Rugendo's easy acceptance of our presence allows the rangers to keep watch over him and his family. But it also allows poachers and soldiers to get dangerously close.

I edge closer, impressed by his brawny arms, many times thicker than a weight lifter's, and salami-size fingers. His massive, furry-crested head holds enormous jaw muscles. While the big chief dozes, Noel and two other sons tussle in mock combat, a favorite gorilla pastime, tumbling, growling, slapping and tugging. The fur on Kongomani and Mukunda, 10- and 12-year-old males, is still black. Noel is especially aggressive, baring his teeth as he repeatedly bangs his fists on the ground and charges his brothers. He leaps on them, pulls at their fur, bites their arms and legs and whacks them on the head. They soon tire of Noel's antics. Now, each time he attacks, one of the brothers grabs him with an arm and tosses him back into the bushes. After a few such tosses, Noel turns to peer at the pale-skinned stranger. Up close his dark brown eyes shimmer.

Along the hike to meet Humba's family a few days later, Serundori points to several circular patches of flattened and bent grass spread around a spray of tall bamboo. "The gorillas slept here last night," he says. A year earlier, I had been with some chimpanzee-like bonobos in Congo about 500 miles to the west. The lithe bonobos live high in trees and construct elaborate nests by weaving branches together. Adult gorillas build nests on the ground that Dian Fossey described as "oval, leafy bathtubs."

After Humba has peered at us through the thicket and resumed feeding, we settle in to watch his clan. The females and youngsters climb out of the undergrowth, stare at us for a few moments, then begin stuffing vine leaves into their mouths. An infant female jumps onto the back of her much bigger brother and whacks him repeatedly on the head, growling in pleasure, until he scurries away. Now and then Humba stops feeding and sits with one hand cupped under his chin, the other resting on an elbow. With his bulging belly, he looks like a sumo wrestler imitating the pose of Rodin's sculpture The Thinker.

Each time the clan moves, a 12-year-old blackback named Nyakamwe plops down between us and his family members, keeping us under watch until they have all disappeared up the slope. He then ambles after them. "He's the sentry," Serundori tells me. "He's there to see them safely away, and to raise the alarm if he thinks we pose a danger." Again and again, Nyakamwe takes up his post, blocking our path until he sees that the others are out of sight.

I listen carefully for the 20 or so sounds that make up gorilla "vocabulary"—growls, grumbles and grunts. WildlifeDirect's de Merode, who has studied gorillas for eight years, interprets for me. A single grunt or a resounding belch means all is right with the world. But watch out, de Merode says, if a gorilla emits what researchers call a pig grunt—part growl and part grunt uttered with bared teeth. It means he is annoyed.

At hour's end, I reluctantly head down the slope. When we encounter the Rwandan Army patrol that had crossed into Congolese territory, I heed de Merode's warning not to take any photographs. But I approach the most important-looking soldier and offer a handshake. He seems unsure what to do and fingers the butt of his machine gun. After a few tense moments, my wide smile and "G'Day mate, howya goin'?" evoke a cautious smile. As the soldier tentatively shakes my hand, de Merode says, "We'd better leave before anything bad happens."

The Congo mountain gorillas' future depends largely on the militias. At U.N. peacekeeping troops' headquarters in Goma, Brigadier General Behl tells me why a quick resolution of the conflict is unlikely. "It's a very difficult task for the [Congo] government," he says, frowning. "It's a long way before they can bring all these groups back into the mainstream."

Paulin Ngobobo, the senior warden of Virunga National Park's southern sector, says that even though President Kabila has promised to protect the mountain gorillas, "after two civil wars, our country is very poor, and we need outside support to save them." WildlifeDirect, the Frankfurt Zoological Society and other conservation organizations are helping the park financially, he says, but much more needs to be done to combat the military threat.

Leaving Ruhengeri, I take a last look at the Virunga Mountains, shimmering like blue glass in the misty air. On the other side of those steep slopes, Humba, Rugendo and their families are playing, mating, caring for their young or sleeping off a hefty snack. How long their serenity continues depends on the courage of the people who protect them, the goodwill of the world to help and the willingness of rebel militias and army troops to leave them alone.

The shocking news came at the end of July. Four mountain gorillas in Congo had been killed by unknown assailants, for reasons unknown. As details trickled out, I learned that the dead were among the mountain gorillas I had visited: Rugendo and three females from his group, Neeza, Mburanumwe and Safari. In August, the remains of the group's last adult female were found; her infant is presumed dead. It was the worst massacre of mountain gorillas in more than 25 years. Rangers tracked down six survivors, including Noel, Mukunda and Kongomani, who was caring for Safari's infant. MGVP vets are now caring for the youngster in Goma.

Rugendo had what I perceived to be a gentle nature, allowing me to approach close to him while he ate leaves and as his offspring played nearby. He was so trusting of humans that he even fell asleep in front of me. The villagers and rangers who knew Rugendo obviously respected him. About 70 villagers carried the mountain gorillas' massive bodies from the forest to bury them near the Bukima patrol post.

Paul Raffaele has written about bonobos, wild dogs, hippos, pirates, cannibals and extreme polo for Smithsonian.