This article examines the history and effect of the Consensus Development Program (CDP) at the National Institutes of Health (NIH). Introduced at a time when the relationship between the U.S. public and the medical profession was at a nadir, the CDP frequently placed the NIH in the middle of broader debates in medical practice and health policy during the last quarter of the 20th century. Drawing on published and archival sources, this paper sheds light on the challenges associated with collecting, assessing, and communicating evidence to medical professionals and convincing them to act on it in the name of improved health care. Administrators at the NIH sought a middle ground between changing medical practice and respecting professional autonomy, with varying degrees of success. This debate has continued implications today as tensions persist between scientific guidelines and the clinical medicine practiced by physicians and expected by patients.