In Cambridge, under Krebs’ mentorship Edson conducted an extensive investigation on the metabolism of ketone bodies, substances produced in excess by humans during starvation or undiagnosed diabetes. Some of these studies (Edson and Leloir, 1936) were a link in a chain of experiments leading to Krebs' 1937 proposal of the citric acid cycle. During the same period Edson identified the product of purine ring formation in pigeon liver as hypoxanthine, which was converted to uric acid in the liver (Edson, Krebs and model,1936; Edson,1946). A derivative of hypoxanthine was subsequently shown by others to be the key product of purine biosynthesis. Krebs became Edson's lifelong friend, a long-range source of scientific advice, a host for his future postgraduate students and his own sabbatical in 1956 (see Krebs, 1981). Edson also befriended Luis Federico Leloir to whom he dedicated his 1966 paper on glucogenesis from sorbitol to celebrate Leloir's 60th birthday.