Syphilis
From 1932 to 1972, the United States Public Health Service did a study on syphilis in Alabama. They wanted to see how syphilis got worse when it was not treated. The researchers chose a group of poor African-American sharecroppers, but never told them they had syphilis. Even after the 1940s, when the researchers knew penicillin could cure these people, they refused to let them get treatment or even tell them that penicillin could help them. This study, now called the Tuskegee syphilis experiment, was very important in creating medical ethics.