That conclusion was reached after the Institute of Medicine, an independent nonprofit organization, found that "most current biomedical research use of chimpanzees is not necessary."
Chimps share as much as 98 percent of humans' DNA, and are our closest relatives. As such, they have been prime candidates for medical and scientific tests.
Opponents, however, say that the practice is cruel and ineffective for developing new medical breakthroughs.
They hope that an NIH decision to retire most of its chimps would lead other private institutions to see the writing on the wall and follow suit.
The NIH decision comes two weeks after the Fish and Wildlife Service declared that all chimpanzees should be considered endangered. Previously only those in the wild were endangered; chimps in the wild were classified as "threatened," which carries fewer restrictions.