Since 1968 the number of postdoctoral research fellows with M.D.s or other professional degrees has fallen from about 4100 to 1730 in training each year. By 1980, the number of M.D. postdoctoral fellows entering and completing research training was about 850 per year. During the past 12 years, the number of M.D.-Ph.D. trainees has risen to about 650 in the federal Medical Scientist Training Program (MSTP) and about 500 in non-federal programs. The attrition rate in non-federal M.D.-Ph.D. programs has been shown to be 44 per cent, and that from the MSTP, 9 per cent. When the length of the training program, the attrition rate, and other factors are considered, present trainees will account for about 150 M.D.-Ph.D. graduates annually in the immediate future. Current training programs can meet only about half the estimated national need for physician researchers. The federal M.D.-Ph.D. program should be expanded to ensure that the country's future research and teaching needs will be met. (N Engl J Med. 1981; 304:1265–8.)