Rosalyn Yalow won the Nobel Prize in 1977 for her work in discovering the radioimmunoassay, which uses radioactive isotopes to detect levels of biological and chemical compounds in the human body. Yalow was the only woman out of four hundred faculty and teaching assistants at the University of Illinois at Urbana, where she earned her PhD in physics in 1945. Unable to find a research institution that would hire a woman, she began teaching physics at Hunter College. In 1947, she began working with a new project in nuclear medicine at the Bronx VA Hospital, becoming assistant chief in 1950. Collaborating with Solomon Berson, she began measuring radioactive iodine in the treatment of thyroid disease, leading to their discovery of RIA, which could be used to measure insulin levels, bacteria, and a variety of other substances in the human body. In 1970, she became chief of the nuclear medicine service and, in 1972, senior medical investigator of the Veterans Administration. In 1973, after Berson’s death, she became director of the lab they had shared and renamed it for him. She also taught at Yeshiva University, and only finally retired from her many positions in 1992.