The experiments, aimed at testing whether penicillin could prevent syphilis, were discovered by a professor of women's studies at Wellesley College in Massachusetts.
The United States apologized on Friday for an experiment conducted in the 1940s in which US government medical researchers deliberately infected Guatemalan prison inmates with syphilis.
Secretary of state Hillary Clinton, Health and Human Services secretary Kathleen Sebelius and other top officials issued a statement about the experiment, which echoed the infamous 1960s Tuskegee study in which black American men were deliberately left untreated for syphilis.
"The sexually transmitted disease inoculation study conducted from 1946-1948 in Guatemala was clearly unethical," the statement reads.
"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 experiments, aimed at testing whether penicillin could prevent syphilis, were discovered by Susan Reverby, professor of women's studies at Wellesley College in Massachusetts.
"In 1946-48, Dr John C Cutler, a Public Health Service physician who would later be part of the Syphilis Study in Alabama in the 1960s and continue to defend it two decades after it ended in the 1990s, was running a syphilis inoculation project in Guatemala, co-sponsored by the PHS, the National Institutes of Health, the Pan American Health Sanitary Bureau (now the Pan American Health Organisation), and the Guatemalan government," she wrote.
"It was the early days of penicillin and the PHS was deeply interested in whether penicillin could be used to prevent, not just cure, early syphilis infection, whether better blood tests for the disease could be established, what dosages of penicillin actually cured infection, and to understand the process of reinfection after cures."
The prison inmates were deliberately infected by prostitutes, but were treated with penicillin afterwards.
Dr Francis Collins, director of the US National Institutes of Health, said regulation prohibited such "risky and unethical" research today.
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