According to Professor Philip A. Pecorino, published in 2002:
Mentally retarded children housed at the Willowbrook State School in Staten Island, New York, were intentionally given hepatitis in an attempt to track the development of the viral infection. The study began in 1956 and lasted for 14 years. The researcher also wanted to determine the effectiveness of gamma globulin injections as protection against hepatitis. They justified their deliberate infections and exposures by claiming that given that there was a high rate of infection in the institution it was practically inevitable that the children would become infected. (Source)
Below, you will find FOIA documents requested on this topic.
Willowbrook Hepatitis Experiments, 2009 [4 Pages, 0.2 MB] – Education material released by the National Institute of Health