U.S. government agency that conducts or supports biomedical research. It is made up of numerous specialized institutes (e.g., National Cancer Institute; National Heart, Lung, and Blood Institute; National Institute on Aging; National Institute of Child Health and Human Development; and National Institute of Mental Health). Part of the Department of Health and Human Services, it also trains health researchers; disseminates information; and maintains other offices and divisions, the National Library of Medicine (the foremost source of medical information in the U.S.), and several research centres