The U.S. National Institutes of Health (NIH) is effectively ending its support for invasive research on chimpanzees. In a memo leaked this week, agency head Francis Collins says that a colony of 50 chimps it had planned to keep in reserve for research—after retiring the rest—is no longer needed.

“I think it is the natural next step in what has been a process over the last 5 years, really, of deep thinking about the appropriateness of research on our closest relatives, the chimpanzees,” Collins tells Science.

The news got out to the press today after someone at NIH leaked an internal staff email from Collins sent on Monday. In it, he wrote that several factors, including the fact that no researchers have asked to use chimps, led him to conclude that the 50 chimpanzees are no longer needed. “Given this complete absence of interest in a space now approaching 3 years, I think it’s fair to say the scientific community has come up with other ways to answer the kinds of questions they used to ask with chimpanzees,” Collins tells Science.

Many countries have banned invasive research on chimpanzees. In 2013, NIH announced it would phase out most agency-funded chimpanzee research and retire most of its 360 research chimps. It planned to keep only a colony of 50 animals in case they were needed in the future. As NIH-funded chimpanzee grants ended, investigators would need to meet new standards to continue.

A decision in June by the U.S. Fish and Wildlife Service (FWS) to list captive chimpanzees as endangered added another hurdle by requiring a permit to use any of the 700 research chimpanzees in the country in invasive research. Researchers would also have to show that the research would somehow benefit chimpanzees in the wild.

As a 14 September deadline approached for the FWS requirement, the agency had not received a single research permit application. And NIH has only received one research application—a proposal from an intramural researcher that was later withdrawn, Collins says.

As he describes in the 16 November leaked email to James Anderson, director of the NIH Division of Program Coordination, Planning, and Strategic Initiatives, Collins lists other factors behind his decision. These included the fact that in 2013, Congress lifted a cap on how much NIH can spend on supporting chimpanzee retirement; and Chimp Haven in Keithville, Louisiana, a sanctuary where retired NIH chimps are being moved, has space for about 25 animals and could potentially take more later.

Collins has asked Anderson’s office to prepare a retirement plan for the 20 or so chimps NIH still owns at the Southwest National Primate Research Center in San Antonio, Texas, and 140 at MD Anderson Cancer Center’s primate facility in Bastrop, Texas. About 150 at the Alamogordo Primate Facility in New Mexico will be moved later because they are further from Chimp Haven, Collins says. The sanctuary doesn’t yet have capacity for 300 more chimpanzees. “We still have work to do,” he says. But it will be easier, he says, “without having to go through the complicated calculus of which chimps ought to be in the group of 50 to be saved for research.”

Collins also asks Anderson to plan for phasing out funding for about 82 chimpanzees at the Southwest center that it supports but does not own.

It’s “amazing and historic news,” says Kathleen Conlee, vice president of animal research issues for The Humane Society of the United States in Washington, D.C., which has pushed to end invasive chimp research.

But Peter Walsh, an ecologist at the University of Cambridge in the United Kingdom, is disappointed. Walsh says it will now be difficult for his group to find chimpanzees for testing an Ebola vaccine to protect wild gorillas and chimpanzees. In a small trial, an injected candidate vaccine was safe and stimulated an immune response. His group now wants to do further trials before deploying the vaccine in Africa. But the facility where he has been testing it, the New Iberia Research Center run by the University of Louisiana, Lafayette, is now thinking about ending its chimpanzee research because of lack of demand for the animals, according to Walsh. NIH’s 50-chimp colony had been a possibility, he suggests, but no longer.

Unless he can drum up private funding to support a colony of chimpanzees for conservation studies, Walsh says, “We are screwed. Rather, the wild gorillas and chimps are screwed.”

Collins, however, notes that Ebola vaccines had only been tested in macaques before they were used in human trials during the recent Ebola outbreak. “It’s not totally clear to me that one would need to do that same kind of testing in a group of captive chimpanzees before offering this in the wild.”