Gerty died in 1957 and Carl married Anne Fitzgerald-Jones (1909-2006) in 1960. He stayed on at Washington University until 1966, when he retired as chair of the biochemistry department. He was appointed visiting professor of Biological Chemistry at Harvard University while maintaining a laboratory space at the Massachusetts General Hospital, where he pursued research in genetics. From 1968 to 1983, he collaborated with noted geneticist Salomé Glüecksohn-Waelsch of the Albert Einstein College of Medicine in New York, until the 1980s when illness prevented him from continuing. In 1976, Carl received the Laurea honoris causa in Medicine from the University of Trieste.