The U.S. government apologized Friday for a previously unreported experiment that infected hundreds of un-consenting Guatemalans with syphilis in the 1940s.

The research was “clearly unethical,” U.S. Secretary of State Hillary Clinton and Health and Human Services Secretary Kathleen Rebellious said in a joint statement. “Although these events occurred more than 64 years ago, we are outraged that such reprehensible research could have occurred under the guise of public health.” Contemporary U.S. research standards require informed consent from study participants as well as approval from an institutional review board.

Guatemalan President Alvaro Colom has called the tests “crimes against humanity,” BBC News reported.

The research was uncovered by Susan Reverby, a professor of women’s and gender studies at Wellesley College. She found that between 1946 and 1948, 696 individuals at the Guatemala National Penitentiary, the National Mental Health Hospital and military barracks in Guatemala were exposed to the sexually transmitted disease (the prisoners via infected prostitutes and the others via direct inoculation). “Permissions were gained from the authorities but not individuals, not an uncommon practice at the time,” Reverby noted in a synopsis [pdf] of a forthcoming Journal of Policy History paper on the subject. The individuals were then given penicillin to see if it would cure the disease, but whether it worked on all subjects “is not clear,” she wrote in the synopsis.