US government medical researchers intentionally infected hundreds of people in Guatemala, including institutionalized mental patients, with gonorrhea and syphilis without their knowledge or permission more than 60 years ago.
Many of those infected were encouraged to pass the infection onto others as part of the study.
About one third of those who were infected never got adequate treatment.
On Friday, Secretary of State Hillary Clinton and Health and Human Services Secretary Kathleen Sebelius offered extensive apologies for actions taken by the U.S. Public Health Service.
"The sexually transmitted disease inoculation study conducted from 1946-1948 in Guatemala was clearly unethical," according to the joint statement from Clinton and Sebelius. "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. We deeply regret that it happened, and we apologize to all the individuals who were affected by such abhorrent research practices."
The apology was directed to Guatemala and to Hispanic residents of the United States, according to officials.
A telebriefing with Dr. Francis Collins, director of the National Institutes of Health and Arturo Valenzuela, Assistant Secretary of State for Western Affairs is expected around 11 a.m. ET.
The episode raises inevitable comparisons to the infamous Tuskegee experiment, the Alabama study where hundreds of African-American men were told they were being treated for syphilis, but in fact were denied treatment. That U.S. government study lasted from 1932 until press reports revealed it in 1972.
The Guatemala experiments, which were conducted between 1946 and 1948, never provided any useful information and the records were hidden.
They were discovered by Susan Reverby, a professor of women's studies at Wellesley College, and was posted on her website.
According to Reverby's report, the Guatemalan project was co-sponsored by the U.S. Public Health Service, the NIH, the Pan-American Health Sanitary Bureau (now the Pan American Health Organization) and the Guatemalan government. The experiments involved 696 subjects - male prisoners and female patients in the National Mental Health Hospital.
The researchers were trying to determine whether the antibiotic penicillin could prevent early syphilis infection, not just cure it, Reverby writes. After the subjects were infected with the syphilis bacteria - through visits with prostitutes who had the disease and direct inoculations - Reverby notes that it is unclear whether they were later cured or given proper treatment.
Reverby, who has written extensively about the Tuskegee experiments, found the evidence while conducting further research on the Alabama syphilis study.