I HE'ethnicity of disease'has been a persistent preoccupation of American medical research, undoubtedly because of die pluralistic composition of diis nation. 1 Throughout American history die peculiar physical characteristics and disease susceptibilities of Negro slaves and freedmen, Indians, and successive immigrant groups have been recorded and analysed by physicians and odiers in direct contact with these groups. Today racially oriented medical studies easily attract popular attention; everyone has heard, for example, diat blacks are prone to hypertension and sickle cell anemia, diat venereal diseases are unduly prevalent among them, and diat dieir cancer survival rate compares badly widi diat of whites. The question of racial influence certainly has a legitimate medical interest. However, racial studies have always been beset by extraordinary hindrances to the achievement of scientific objectivity and factual documentation. Researchers on tuberculosis struggled against scientific difficulties as well as the distortions created by dieir own prejudices as over the course of a century they repeatedly turned their attention to die manifestations of tuberculosis in American blacks. Their investigations encompassed a number of the disciplines of scientific medicine, because die Negro was both a major key to the etiology of tuberculosis and a serious problem in dierapeutics and public healdi. Most of the pitfalls and potential value of racial research are illustrated in die study of tuberculosis among Negroes.