The United States government has apologised for deliberately infecting hundreds of people in Guatemala with gonorrhoea and syphilis as part of medical tests more than 60 years ago.
None of those infected - mentally ill patients and prisoners - consented.
Guatemalan President Alvaro Colom accused the US of "crimes against humanity".
US President Barack Obama has called Mr Colom to apologise and has said the acts ran contrary to American values.
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We deeply regret that it happened, and we apologise to all the individuals who were affected by such abhorrent research practices”
Statement from secretaries of state and health
'Shocking, tragic, reprehensible'
Syphilis can cause heart problems, blindness, mental illness and even death, and although the patients were treated it is not known how many recovered.
Evidence of the programme was unearthed by Prof Susan Reverby at Wellesley College. She says the Guatemalan government gave permission for the tests.
No offer of compensation has yet been made, but an investigation will be launched into the specifics of the study, which took place between 1946 and 1948.
http://www.bbc.co.uk/news/world-us-canada-11454789