He began his postdoctoral work at the National Institutes of Health (NIH) in 1957 as a fellow of the American Cancer Society in what was then called the National Institute of Arthritis and Metabolic Diseases. In 1959 he became a research biochemist at the NIH and began to study the steps that relate DNA, RNA and protein. Nirenberg's groundbreaking experiments advanced him to become the head of the Section of Biochemical Genetics in 1962 in the National Heart Institute (now the National Heart, Lung, and Blood Institute), where he remained a laboratory chief until his death. Fellow laboratory chiefs included Ernst Freese and Daniel Carleton Gajdusek. He was married in 1961 to Perola Zaltzman, a chemist from the University of Brazil, Rio de Janeiro, who also worked at NIH and died in 2001. Nirenberg married Myrna Weissman, Ph.D., Professor of Epidemiology and Psychiatry at Columbia University College of Physicians and Surgeons in 2005. He had four stepchildren: Susan Weissman of Evanston, Illinois, Judith Weissman of New York, New York, Sharon Weissman of New Haven, Connecticut, and Jonathan Weissman of San Francisco, California. He was also survived by his sister, Joan Nirenberg Geiger of Dallas, Texas, several nieces and a nephew.