Alex Leaf has led a rich and deeply rewarding life. His activities have included a highly successful career as investigator in the fields of epithelial transport, renal electrolyte metabolism and preventive medicine. He has been an outstanding chairman of one of the most prestigious departments of medicine, been in the forefront of medical education, and has throughout his life been deeply concerned with humanitarian issues. Alex was born in Yokohama where his parents had emigrated from Russia, but received his primary and college education in Seattle where his family moved from Japan in the early 1920s. Both of his parents were dentists, and they provided an early environment of stimulation, encouragement and support for Alex and his older brother. Alex also has fond memories of the beautiful scenery of the Northwest, with boat trips and fishing, and lingering memories of early biological activities including oceanographic explorations at Friday Harbor. These were marred only by severe seasickness. It was also at Friday Harbor that Alex met Barbara, the daughter of a prominent professor of zoology at Washington University, to whom he was married in 1943. Alex graduated from the University of Washington with magna cum laude in chemistry and entered medical school at the University of Michigan in 1940. During his first year in medical school at Ann Arbor, he had the good fortune to befriend David Newburgh, the son of a distinguished professor of internal medicine. He came close to being adopted by the Newburgh family and through Professor Newburgh's strong influence Alex's career took an early turn towards internal medicine. His next career stations included an internship at the Massachusetts General Hospital, residency at the Mayo Foundation and Army service at El Paso, Texas, before returning for a two-year research fellowand instructorship in internal medicine in Michigan. There he joined Dr. Newburgh's laboratory, and that is where his scientific career began. In Alex's first work in Michigan, he explored the mechanisms of renal sodium and potassium handling by the human kidney, focusing on balance studies and on the impressive ability of the kidney to retain sodium during prolonged salt restriction. These studies already show the mark of his approach: asking an important question, thorough attention to analytical detail and prudent interpretation of the data. Such studies were continued after Alex moved to the Massachusetts General Hospital in 1949. He had received a National Research Council fellowship after successful competition and personal scrutiny by such notables of medicine and physiology as Baird Hastings, Robert Loeb and Homer Smith. At the Massachusetts General Hospital he joined the laboratory of the eminent endocrinologist Fuller Aibright, where he explored