Buffeted by high winds as he clung to a steep slope near the top of the world, Gabriel Willmann saw that his clothes were covered in an inch-thick layer of ice. It was after midnight, and he had lost track of his climbing partner. Nearby, the light from his headlamp revealed a dead body left by a past expedition, not uncommon on the world's highest peak.

But his immediate concern was what he'd find when he checked on his other companions:

Huddled in a small cage in his backpack were eight white laboratory mice.

This was extreme science, Mount Everest edition.

Willmann and his boss, Tejvir Khurana, made it back this month to their University of Pennsylvania lab, where they described their experiences last week. Their bodies were spent from the formidable climb to near the top of the ice-encrusted peak, yet their work had just begun, as they waited for vials of mouse blood to be shipped home.

The goal is to develop a blood test to catch athletes who have improperly boosted their ability to carry oxygen - one of many illicit techniques that have cast a pall on events from the Tour de France to the Olympics.

No one minds if athletes gain an edge by living at high altitude, which has been shown to increase the body's number of red blood cells. It's the ever-growing menu of artificial methods that draws scrutiny.

The Penn researchers, funded primarily by the World Anti-Doping Agency, believe they can identify subtle molecular signals to distinguish the clean from the dirty.

They carried mice up Everest - cleaning their cages daily near the end - to gauge the impacts of high altitude. Now they will compare the blood from those mice with that of others that have been exposed to drugs, low-oxygen "chambers," and even genetic manipulation - which the agency predicts will be used someday by athletes, if it is not already.

Khurana, 47, grew up in the Himalayas, where his father was an officer in one of the famed Gurkha mountain regiments. He has been climbing since he was a teenager, scaling summits in Africa, South America and Asia.

Willmann, 30, a physician researcher in Khurana's physiology lab, is from Germany. He regularly climbs the Alps and once mountain-biked 6,500 miles from his homeland to Ivory Coast.

"In some ways, we were uniquely qualified for this," said Khurana, a compact, wiry man who likes to wear running shoes and shorts in his West Philadelphia office.

Last year the two scientist-climbers did experiments with fruit flies on the top of Alaska's Mount McKinley, also known as Denali. In 2005, they took mice partway up Chile's Mount Marmolejo, in the Andes, to study how low oxygen levels affect muscle function.

Before this year, neither had tackled the world's highest mountain, but a colleague had. Penn physiologist Sukhamay Lahiri, 75, is a veteran of seven research trips to Everest, including one in 1960 with Sir Edmund Hillary, one of the men who first reached the top in 1953.

Like his younger colleagues, Lahiri had tried to simulate high-altitude conditions in the lab. But Khurana and Willmann agreed with him that it was a poor substitute for mountain air. For example, in Lahiri's final trip in 1981, the air pressure on Everest did not correspond with what was predicted in the lab. "It's better to do the real thing," Lahiri said. "You go to the mountain."

So on April 11, with more than 260 pounds of gear in tow and Lahiri's words of encouragement in their ears, Khurana and Willmann were off to Nepal.

Politics and chaos

The duo's first choice had been to take the easier, less expensive route to the top from Tibet, but Khurana's requests were rebuffed by the Chinese government.

So they started instead from Nepal, where the streets of Kathmandu were full of flag-waving demonstrators, celebrating the Maoist victory in national elections. Within weeks, the new government would vote to dissolve the monarchy, giving the king 15 days to leave his throne. Despite the chaos, the necessary climbing permits were signed.

Still, the neighboring Chinese posed a problem. Worried that protesters would interfere with climbers who were taking the Olympic torch to the summit, they had closed the Tibetan side of the mountain. Even on the Nepalese side, the Chinese demanded that no one climb past 21,000 feet until after May 10. Nepalese regiments were stationed with rifles to enforce China's wishes, Khurana said.

The two scientist-climbers got 16 mice from collaborator Rohit Pokharel, a Nepalese physician who flew with them to the town of Lukla and did the first leg of the hike. On the mountain, the duo met their two Sherpa guides - one of them named Tenzing, like the man who joined Hillary on his famous climb.

Then began several careful stages of acclimatization - climbing up to a certain point, then retreating back several thousand feet to adjust. If not, they could have suffered serious harm or even death from ills such as excessive fluid in the lungs.

"Just getting out of the tent is difficult," Willmann told a family member by satellite phone from 21,000 feet.

The climbers wore the latest in cold-weather gear; the mice were in an insulated cage with heating pads.

The plan was to take blood at two points - partway up, and as near the top as possible - to measure changes.

At 17,400 feet, the scientists anesthetized eight mice and removed all of their blood, so it could be studied back in Philadelphia.

But two weeks later, as the climbers prepared to head to the summit, there was a setback: The remaining mice died from cold. So they called for replacements, waiting a week for a courier to bring them.

Finally, on the night of May 27, it was time to go for the top. Willmann and Khurana climbed separately, each with one of the Sherpas.

Willmann carried the mice in his pack. A half-hour past midnight, he neared 28,000 feet, where the amount of oxygen in the air is one-third the level in Philadelphia.

Unknown to him, Khurana had decided to turn back farther down.

In the glow from his headlamp, Willmann saw what he thought was an abandoned oxygen bottle. With a start, he realized it was the boot on the body of a climber who had perished in a past expedition. Death is common on Everest - about one for every 10 successful ascents, according to an analysis cited in the British Medical Journal - and often the bodies cannot be carried down.

Worried about the mice, Willmann took off his gloves so he could open the cage. Indeed, one more had died, and the remaining seven seemed to be weakening.

To finish the experiment, the mouse blood had to be drawn while the animals were alive, so the genetic material would not decay.

Still, Willmann felt good, and he was within 1,000 feet of a tantalizing feat - the summit of Mount Everest.

What should he do?

Limits and signals

For decades, climbing above 26,000 feet - the "death zone" - was thought to be impossible without the use of oxygen bottles.

Then two climbers did it on Everest in 1978, sparking renewed interest by physiologists in the limits of the human body.

When the brain senses that oxygen is growing scarce - a condition called hypoxia - it sends a signal to the lungs to breathe faster. The thin air also prompts the kidneys to produce more of a hormone called EPO. This in turn stimulates the production of oxygen-carrying red blood cells.

Some athletes have tried to mimic this effect by secretly taking synthetic EPO, although a new study questions the accuracy of a urine test used to detect it. Other drugs fool the body into making its own EPO, or into sprouting new blood vessels.

The various chemicals have their origin in legitimate uses, such as treating anemia, but the sports world maintains a keen interest. When Khurana wrote a paper on how blocking a certain protein caused muscle growth, his e-mail box was flooded - half the messages from sick patients, half from athletes seeking a competitive edge.

A study by WADA, the anti-doping agency, found that in 2006, about 2 percent of samples tested in Olympic sports indicated use of banned substances, from steroids to EPO. It is widely thought that other drugs are being used for which there are no tests.

A legal alternative is low-oxygen chambers, or "tents," favored by cyclists, runners, and some members of the Philadelphia Flyers. But WADA plans to study the devices more, having found them to violate the "spirit of sport."

Khurana's primary research is the study of muscular disease. But as an athlete, he feels strongly about the use of drugs in sports, because of both potential harm and the issue of fairness.

"For me, it's a very black-and-white issue that the playing field should be level," the Penn researcher said.

As for low-oxygen tents, he called that "more of a gray area." He is interested in whether they are safe or even effective, and whether he can tell the difference between the blood of someone at altitude and someone who has used a tent. He will do that by testing which genes have been switched on or off in response to the environment. He expects to have results in a few months.

One thing the chambers certainly cause is faster breathing. In Khurana's lab at Penn last week, a brown mouse sat in a small version. In normal air, the creature breathed two or three times a second. When the oxygen was lowered by a third, the mouse breathed faster: four to five times a second.

Yet no mice had ever been anywhere near the top of the world's tallest mountain, Khurana said, and no one knew if they could make it.

Back down

The wind reached 45 m.p.h., whipping snow crystals into the black sky.

Willmann could see the animals were cold, and their heating pads seemed to have stopped working. So he took the pads from his gloves and put them in the cage.

"It worked," he recalled. "They sat on it."

But he was worried they wouldn't last much longer. Not knowing where Khurana was, after 45 minutes Willmann finally turned back.

Khurana was below Willmann at the time; unsure whether his younger companion was headed up or down, and fearing hypothermia in the icy winds, he descended to a temporary shelter at 26,000 feet. Willmann joined him soon after.

"So close to setting foot on top of the world," Willmann wrote later on his blog.

But science was the main goal, and they had succeeded. They'd taken lab mice higher than anyone before.

After two hours of rest, the climbers started down and once again collected mouse blood. They used a chunk of ice from the mountain to keep the samples fresh.

They reached base camp the next day, and on May 29, they began the hike to the airstrip to catch the flight to Kathmandu. The vials of blood would be shipped later.

Back at Penn for a few days before jetting to Switzerland to speak about his research, Khurana admitted to some disappointment about stopping short of the summit. Yet he said it was not a difficult decision.

"You're always going to have more peaks that you don't climb than peaks that you climb," he said. "I think people get in trouble where they want it so much that they don't turn back."

What Khurana wants is knowledge, and soon it will arrive, in the form of a FedEx package from the other side of the world.

A brief video from Mount Everest, and a blog with more photos: http://go.philly.com/healthEndText