The decision, which follows the recommendations of an agency advisory group, does not end biomedical research on N.I.H. chimpanzees. But it calls for retiring about 310 animals that the agency owns over the next few years, to sanctuaries from which they cannot be recalled for research. A colony of up to 50 will be kept at a site yet to be decided in case there is a compelling need to use them in research for human health. And new guidelines will be in place for any future research and for chimpanzee housing.