He studied rodents that received lethal doses of radiation who were then saved by an infusion of marrow cells at Mary Imogene Bassett. At the time, patients who underwent bone marrow transplantation had all died due to either infections or immune reactions that were not seen in the rodent studies. He began to use dogs as a model system. He moved his lab to the United States Public Health Service in Seattle in 1963. In 1990, he received the National Medal of Science. He was one of 22 Nobel Laureates that signed the Humanist Manifesto in 2003.