Tuskegee syphilis experiment
During World War II, 250 of the Tuskegee men registered for the draft.  These men were given medical exams by the military, and were diagnosed as having syphilis.  They were ordered to get treatment for syphilis before they could be taken into the military. But the Tuskegee study's researchers tried to keep these men from getting treatment.  A Public Health Service worker was quoted at the time saying: "So far, we are keeping the known positive patients [the men with syphilis] from getting treatment."