During the 1940s, in Britain, there was great activity in the field of social medicine. This was generated by an upsurge in interest in social issues and a desire to promote occupational health research. In 1948 the Medical Research Council established a Social Medicine Research Unit. The background to the creation of the Unit and its early work are discussed. By the early 1950s, the political atmosphere had changed and criticisms of the Unit's work during the debate about continued funding in 1952 are considered. Important work on the relationship between coronary heart disease and physical exercise, and the results of a study of infant mortality, were published in the mid-1950s. A brief account of the subsequent history of the Unit, until its closure in 1975, is given.