In 1946, American researchers performed an appalling experiment, infecting unwitting Guatemalans with a potentially deadly disease in the name of public health.
In an effort to see if penicillin could prevent or treat syphilis, government scientists went to the impoverished Central American country to deliberately infect nearly 700 men and women -- including prisoners, inmates in insane asylums, and even some soldiers -- with the potentially fatal sexually transmitted disease.
The researchers used prostitutes to infect the men and hypodermic needles to infect the women.
Watch "World News" for more on this story tonight on ABC.The experiments, which lasted from 1946 to 1949, were uncovered last year by Susan Reverby, a professor at Wellesley College, as she was researching a book.
When she came across the Guatemala study, her first reaction was, "Oh my God, Oh my God, Oh, my God," Reverby told ABC News today.
"The evidence is clear that [the subjects] didn't know. The authorities were told something, but the people didn't know," she said.
President Obama himself spoke with the president of Guatemala, Alvaro Colom, via phone today to express "deep regret" over the study, the White House said in a statement.
Secretary of State Hillary Clinton and Health and Human Services Secretary Kathleen Sebelius also issued a joint apology today in a written 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. We deeply regret that it happened," the statement read.
A U.S. government official told ABC News today that the National Institutes of Health will launch two panels to examine the Guatemala study.
Guatemala's Ambassador to the United States, Francisco Villagran de León said today that he appreciated the decision for a full investigation.
"We don't even know if there is a list of these individuals. If there are any survivors, which is not likely, we should make sure that they should receive care," the ambassador said.
The experiments are eerily similar to the infamous Tuskegee syphilis experiments on African Americans, also run by the U.S. Public Health Service. Reverby was researching the case when she came across the records from Guatemala.
In the Tuskegee study, which ran from 1932 to 1972, the same American Public Health service researchers studied 400 poor black men in Alabama who already had syphilis. But the men never were told they were sick, and they never were treated for it. Some participants died from the disease.
The effects of the Tuskegee study continues to have a widespread effect on African Americans' confidence in the public health system. A 2008 study found that black Americans are less likely to participate in research studies than whites, a factor that researchers attributed to fears -- rooted in the Tuskegee tests -- that research participants could incur harm.
In the Guatemalan study, run by the same American Public Health Service doctor as Tuskegee, the subjects were given the antibiotic penicillin, though it's not clear whether they received enough and what exactly became of them.
ABC News' Dr. Richard Besser, a former acting director of the Centers for Disease Control and Prevention, said both experiments were highly unethical.
"I think there's absolutely no difference between the Tuskegee experiment and what took place in Guatemala," Besser said. "You had two populations that were mistreated for the benefit of medical knowledge."
Although it was common practice to use unwitting subjects for medical experiments in those days, then-Surgeon General Thomas Parran said about the Guatemala study, "You know, we couldn't do this in this country."
"It used to be that the idea of informed consent -- asking permission -- was unheard of," said Besser. "Sixty years ago, there weren't ethical boards, there weren't institutional review boards reviewing studies determining what you could and couldn't do. It's a different world today."