As monkeys go, sooty mangabeys aren't cute.

Big-fanged, gray and hairy, they simply stare when threatened. Few zoos stock them. Some animal rights advocates can't even spell the species' name.

Nevertheless, the sooties are at the center of a precedent-setting debate over whether researchers should be allowed to experiment on an endangered species.

Scientists at the Yerkes National Primate Research Center in Atlanta have nurtured a group of these primates for decades. But after Yerkes started the colony, federal officials listed sooties as endangered.

The result: Yerkes has the world's largest collection of captive sooties, but with little hope of scientific benefit.

"We don't need them around just to look at them. We're not a zoo," said Thomas Gordon, Yerkes' associate director for scientific programs.

Recently, Yerkes researchers proposed a novel solution: The primate center will help conserve sooties in the wild in exchange for permission to do AIDS-related research on them here.

Such a trade-off has never before been permitted, said Timothy Van Norman, chief of the international permits branch at the U.S. Fish & Wildlife Service. "This is new territory," he said.

Yerkes officials are hopeful. Animal rights activists are horrified.

"It's a deal with the devil," said Rachel Weiss, president of Laboratory Primate Advocacy Group, a Georgia-based animal rights organization.

Yerkes — part of Emory University — is one of eight federally funded national primate research centers. Its scientific contributions include new understanding of monkey and chimp behavior and development of an experimental AIDS vaccine.

It has about 3,600 primates at a 25-acre campus in Atlanta and a 117-acre field station in nearby Lawrenceville.

Yerkes' colony of sooty mangabeys was started in the late 1960s, when the center picked up about 30, some from Kansas City's zoo. The colony grew, and now numbers about 230.

It would be larger, but the Yerkes staff segregate males from females and give females Norplant-like birth control pellets. The center spends roughly $170,000 each year for sooty care-taking, and is out of space to house any more.

In 1988, U.S. Fish & Wildlife listed sooties as endangered. That means Yerkes may not do invasive research, such as a biopsy, unless it benefits the species.

"We can't even take a blood sample for research purposes," complained Preston Marx, a researcher at Tulane University, which also has a sooty colony.

In the 1990s, researchers learned sooties are natural carriers of a monkey-form of the AIDS virus. Other types of monkeys get sick from the virus. Sooties don't. Researchers say if they can learn why sooties stay healthy, it may lead to new weapons against human HIV.

To do that, scientists want to expose the monkeys to different viruses and do biopsies or other invasive research.

For a decade, Yerkes has been asking the government to drop sooties from the endangered list or consider other ways to allow research.

They saw an opportunity when Van Norman, Fish & Wildlife's chief of international permits, suggested the agency might grant the right to research in exchange for supporting conservation of the monkeys in the wild.

Last year, Yerkes began providing up to $30,000 a year to support primatologist Scott McGraw's field-based conservation and research of sooties in the Tai National Park Reserve in Ivory Coast, West Africa.

In July, the center wrote Fish & Wildlife seeking the right to conduct research on the Yerkes sooties "given our contribution to sooty mangabey conservation."

The request is under review, Fish & Wildlife officials said.

The proposal is not completely novel — it echoes the agency's "safe harbor" policy. That allows landowners the prospect of future development of land that serves as habitat for threatened or endangered animals, as long as the animals' original population doesn't fall and other standards are met.

But animal rights advocates are uncomfortable applying such a trade-off to lab animals.

Sooties live in large pens at the Yerkes field station, with some freedom to roam and socialize. But being a research monkey is a "terrible life" that often involves indoor caging and pain, said Weiss, who was a Yerkes animal care technician in the mid-1990s.

"It's a tough call when you talk about conservation of a species versus protecting individuals. But we have to remember individuals comprise a species," she said.

Animal rights groups have criticized Yerkes before. They point to the death of a chimp in 2004. After that happened, a federal inspection of monkey carrier cages led to a fine for lack of proper ventilation.

Also, they argue, experimentation with sooties may not be fruitful.

Chimpanzees were once deemed promising for HIV research, but they don't get sick from HIV. Sooties may be no better than chimps, said Theodora Capaldo, president of the New England Anti-Vivisection Society, one of the nation's oldest groups opposing animal experimentation.

"The thing that concerns me is they (Yerkes officials) have a 'product' — an abundance of monkeys — that they want to do something with, and now they're going to find something to do with them. But that's backwards thinking, the idea that availability drives inquiry," she said.

Yerkes officials say it's hard to predict results of future research, but sooties differ from chimps in several ways, including the amount of virus they naturally carry.

"The sense from the scientists is we need now to move to the next level," Gordon said.