"The U.S. government has apologized for experiments in which government researchers used prostitutes to deliberately infect prison inmates in Guatemala with syphilis."
PDF - preprint: http://www.wellesley.edu/WomenSt/Synopsis%20Reverby%20%27Normal%20Exposure%27.pdf
<http://www.cbc.ca/health/story/2010/10/01/syphilis-guatemala.html#ixzz12DgPOPgP>