101 first transplants were done in patients with end-stage renal disease using kidneys from parents or offspring. All patients were followed up for at least two years, and the absolute two-year patient-survival rate was 88% and the two-year functional-kidney rate was 79%. Actuarial statistics at four years were 82% for survival and 67% for function in the parent-to-child group. In the child-to-parent group absolute patient survival was 83% and transplant function was 79% at two years; these results were unchanged at four years. Thus, transplants from parents to children or from children to parents are much the same despite differences in age. There is some advantage in parent-to-child transplants from being female but no advantage in being diabetic, receiving higher or lower doses of antilymphocyte globulin, or sharing more than two HLA antigens with the donor. Mismatched sibling transplants survived approximately as well as did grafts from parents to children and children to parents. These results, taken in concert with the poor results of cadaver transplantation, the relative safety of donation, the high personal motivation to donate in these groups, and the personal satisfaction derived by the donor, strongly support the policy of informing potential recipients of the benefits of parental or offspring kidney donation.