For the past 4 years (1986 to 1989), there has been virtually no change in the number of organ donors, despite significant efforts targeted toward increasing supply. The number of donors has plateaued at about 4,000 annually. Meanwhile, the number of people awaiting transplants continues to increase at a remarkable rate. Between December 1987 and December 1990, the number of people awaiting a kidney, heart, liver, heart-lung or pancreas transplant increased by 65%. This demand/supply disparity has led to much interest in the assessment of the organ procurement system. Such an assessment must endeavor to compare the supply of potential donors with actual donor procurements. Numerous studies have been conducted to estimate potential donor supply. Some relied upon the review of in-hospital death records, whereas others attempted to search and identify potential donors in large mortality databases. Regardless of their source, patient records are examined and databases searched to exclude those deaths where contraindications to organ donation are present. Due to the severe shortage of donors, exclusion criteria have been relaxed to include deaths of marginal potential donors. Six major studies, all conducted between 1975 and 1991, indicate that the number of potential donors per million population is between 28.5 and 104. The most realistic estimates of supply place the number of donors between 43 and 55 per million population. The range of potential donors is, therefore, somewhere between 7,088 and 25,865. The most realistic range is between 10,694 and 13,679. These estimates must be adjusted further based upon public attitudes toward donation. Between 53% and 68% of the public is willing to donate the organs of relatives under appropriate circumstances. Thus, between 5,700 and 9,300 donors may be available annually. Whereas the demand for extrarenal organ transplantation could conceivably be met, the need for kidney donors is likely to continue to exceed supply. The situation could be improved by encouraging both living-related and living-unrelated kidney donation. Also, further consideration might be given to the possible use of nonheart-beating cadaveric donors.