Following successful kidney transplantation, renal anemia is gradually corrected during the first 3-4 months. Serum erythropoietin (EPO) levels are increased after the first postoperative day following grafting. In this study, the serum EPO levels in the early posttransplant phase were investigated in 8 living-donor and 7 cadaveric-kidney transplant recipients with special emphasis on the first 24 h. Despite a considerable difference in cold ischemic time of the graft in the two groups the increase in serum EPO levels was noticed at about the same time (8 h) in both groups and the first peak of serum EPO, which was observed after 24 h, reached the same level in both groups. After 9-11 days, serum EPO reached levels which usually are observed during the first months following transplantation. The EPO response seems to be blunted in relation to the degree of anemia in the early posttransplant phase.