Dr. Berson, together with Dr. Rosalyn S. Yalow, his long-standing partner in research, introduced the radioimmunoassay of plasma insulin in 1959. Over the next decade the method completely revolutionized the field of endocrinology, both technically and clinically. The revolution spread from polypeptide hormones to the steroid hormones and then, like other great revolutions, spread beyond the confines of endocrinology to involve clinical pharmacology, oncology, virology, and hematology. It is difficult to find a field of medicine or biology that has not been affected. Dr. Berson was born and raised in New York City. He received the Bachelor of Science degree from the City College of New York in 1938, whereupon he entered the graduate schools of New York University. In 1939 he was awarded the Master of Science degree, and following three years in the Department of Anatomy, was enrolled in the School of Medicine, receiving the Doctor of Medicine degree in 1945. In 1948, after having completed one year of internship at the Boston City Hospital, and two years in the US Army Medical Corps, he moved to the Veterans Administration Hospital, Bronx, New York. In 1950, after completing his residency training in internal medicine, he was appointed to the staff of the Radioisotope Service, and became Chief of that unit in 1954. He became Senior Investigator in 1963, a title he held until his death. In 1968 he accepted appointment as Chairman and Murray M. Rosenberg Professor in the Department of Medicine of the Mt. Sinai School of Medicine and Director of the Department of Medicine of the Mt. Sinai Hospital in New York City. In 1951 a paper appeared in Science (114: 14) entitled" The use of K42-tagged erythrocytes in blood volume determinations," by RS Yalow and SA Berson. This was the first of more than two hundred publications that were to appear in the scientific and medical literature over the next twenty years by these coauthors. Their research, which applied radioisotopes to