Citing "new scientific methods and technologies" rendering the use of chimpanzees in research almost — but not quite — unnecessary, the National Institutes of Health announced their intention to retire all but 50 of the chimps they have on hand for research, out of a total of nearly 360. The NIH's press release explains

"NIH plans to retain but not breed up to 50 chimpanzees for future biomedical research...The chimpanzees designated for retirement could eventually join more than 150 other chimpanzees already in the Federal Sanctuary System." 

There's a balance considered by scientists who do research on chimps that, for the NIH, seems to be tipping more and more towards the reduction of the use of the primates, who are genetically similar to humans. On the one hand, there's the usefulness of a genetically similar model to humans for experimentation. On the other hand, there are a host of ethical concerns. Taking the latter into account, the bar set for experimenting on chimpanzees is based on an earlier report by the Institute of Medicine. It governs experiments that would cause harm or mental stress to the animals. Essentially, those experiments will be allowed to use chimps if no alternatives exist, and the research is deemed important enough, a relatively narrow window.  

While the move is dramatic, a further reduction in the number of chimps retained for research would not be so easy: chimpanzees are important for research into for Hepatitis C. They're the only animal, aside from humans, who can catch the virus, so many scientists working on vaccines against the disease would be left without a non-human model if chimps were off the table. Wired has an excellent longform piece on the debate surrounding their use, which will tell you everything you've ever wanted to know about chimps and Hepatitis C. 

An interesting note: the NIH, apparently, will have to petition Congress to get enough funding to retire their chimps into the Federal Sanctuary System, leaving their long-term home a bit up for grabs at the moment.