[2] He interned at Mary Imogene Bassett Hospital in Cooperstown, New York, before returning to the State University as a pediatric medical resident.

As part of the Corps, Parkman worked at Walter Reed Army Institute of Research in Silver Spring, Maryland, where he became interested in virology.

However, when Parkman joined the National Institutes of Health (NIH) in 1963, they showed interest in his research.

[6] As director, he dealt with policies for the testing of HIV/AIDS, approved a bacterial meningitis vaccine, and increased the scrutiny paid to blood banks.

[7] Parkman died of lymphoblastic leukemia at his home in Auburn, New York, on May 7, 2024, at the age of 91.

In 1999, Parkman and his wife donated the piece to the Smithsonian American Art Museum.