The Tuskegee Study, an observational study of over 400 sharecroppers with untreated syphilis, was conducted by the U.S. Public Health Service to document the course of the disease in blacks, and racial differences in the clinical manifestations of syphilis. The men were not told they had syphilis, not given counseling on avoiding spread of the disease, and not given treatment throughout the course of the study. The study became the longest (1932-1972) nontherapeutic experiment on humans in the history of medicine, and has come to represent not only the exploitation of blacks in medical history, but the potential for exploitation of any population that may be vulnerable because of race, ethnicity, gender, disability, age or social class. It is important for physicians who will be caring for an increasingly diverse nation to understand the lasting implications of this study for their patients, but the effects of the Tuskegee Syphilis Study are demonstrated most strikingly by unsuccessful attempts at improving representation of minority patients in clinical trials.