Professional requirements for physicians specializing in nephrology were estimated to assist policymakers in developing guidelines for graduate medical education. In estimating service requirements for nephrology, a nephrology Delphi panel reviewed reference and incidence-prevalence and utilization data for 34 conditions that are treated in the office practice of a nephrologist. After adjusting incidence-prevalence rates, panelists reviewed data on the percentage of persons with each condition requiring health care. Leading ambulatory problems were identified, and delegated visits by condition were estimated. Hospital discharge rates from a discharge survey were compared with 1977 and projected 1990 rates, as determined by the nephrology Delphi panel. The final estimates of the Delphi panel implied that approximately 3,900 to 4,200 specialists would be required in 1990. Based on a generic model, a final estimate of nephrologists required for 1990 was between 2,120 to 2,780. Appendices include: lists of members of the Graduate Medical Education National Advisory Committee and members of other technical panels, information on the procedure for calculating internal medicine subspecialty ambulatory requirements, ambulatory care data from the Delphi panel, reference notes, and a bibliography. (SW)