U.S. government researchers who purposely infected unwitting subjects with sexually transmitted diseases in Guatemala in the 1940s had obtained consent a few years earlier before conducting similar experiments in Indiana, investigators reported [August 29]. The stark contrast between how the U.S. Public Health Service scientists experimented with Americans and Guatemalans clearly shows that researchers knew their conduct was unethical, according to members of the Presidential Commission for the Study of Bioethical Issues. These researchers knew these were unethical experiments, and they conducted them anyway, said Raju Kucherlapati of Harvard Medical School, a commission member. At least 5,500 prisoners, mental patients, soldiers and children were drafted into the experiments, including at least 1,300 who were exposed to the sexually transmitted diseases syphilis, gonorrhea and chancroid, the commission reported. This is a dark chapter in our history. It is important to shine the light of day on it. We owe it to the people of Guatemala who were experimented on, and we owe it to ourselves to recognize what a dark chapter it was, said Amy Gutmann of the University of Pennsylvania, the commissions chairwoman.