Washington: The US National Institutes of Health quietly ended the federal government's long and controversial history of using chimpanzees for biomedical research.

Director Francis Collins announced on Wednesday that 50 chimpanzees held by the US government for medical research will be sent to sanctuaries. His decision came a little more than two years after NIH decided to release more than 300 chimps at research facilities across the country and resettle them in more humane conditions.

Keeli, a chimpanzee at the Ohio State University animal laboratory, looks out from his play room, in Columbus, Ohio in 1999. In 2011, a prestigious scientific group told the US government that chimpanzees should hardly ever be used for medical research. Credit:AP

"It is time to acknowledge that there is no further justification for the 50 chimpanzees to continue to be kept available for invasive biomedical research," Dr Collins wrote to NIH administrators, according to an email sent by a spokeswoman.

The NIH started phasing out its funding and use of research chimps before 2013, when it housed nearly 400 in states such as Texas. "Americans have benefited greatly from the chimpanzees' service to biomedical research," he said then, "but new scientific methods and technologies have rendered their use in research largely unnecessary."