Bell's interests turned to biology in the 1960s, creating quantitative models in immunology. He headed the Theoretical Biology and Biophysics group at Los Alamos from 1974 to 1990. He also worked on mathematical models in biophysics. In 1988, he became the founding director of the Center for Human Genome Studies, which became a major participant in the Human Genome Project. He was director for only one year (simultaneously acting as the head of T Division and the group leader for the Theoretical Biology and Biophysics group), and retired from Los Alamos in 1990. He continued to work as an associate of the laboratory until September 1999.
