During the 1960s, the US National Institutes of Health moved federal prisoners from penitentiaries across the country to the NIH main campus in Bethesda, Maryland to serve in clinical studies of viruses, including simian virus-40 (SV40). Federal researchers at the NIH hospital were interested in SV40 because it was known to cause cancer in animals, and yet it was unclear how the virus affected humans. Millions of Americans, however, had received polio vaccines between 1954 and 1961 that contained SV40. Thus, in the early 1960s, prisoners in the wards of Dr. Vernon Knight, clinical director of NIH's National Institute of Allergy and Infectious Diseases, were used in studies of SV40.

This paper has two aims. First, the paper provides a comprehensive history of the NIH prisoner program by reviewing the studies of SV40 on inmates moved to Bethesda. To do so, the paper draws in published primary sources and unprocessed manuscripts from the public records of the US National Institutes of Health. Second, it connects the history of cancer-virus studies to the history of clinical research, which historians have often treated separately. The prisoner program at NIH helps to flesh out what scientists came to learn, overlook, and imagine about cancer viruses through federal research programs. In so doing, the paper links themes in the philosophy of science, particularly the ontology of natural kinds, to the practice of history writing.