We studied production of erythropoietin (EPO) in long-term renal allograft recipients with posttransplant erythrocytosis (PTE). Among 95 I recipients we found 74 patients with persistent elevation of hematocrit (Htc) value (female >50%, male >55%). However, only 63.5% of them had increased red-cell mass (="true" erythrocytosis). In all recipients with PTE known causes of secondary erythrocytosis were not found. EPO titer in peripheral blood was significantly higher in recipients with PTE (median 13.5 mIU/ml, range: 0.1-71.5 mIU/ml) as compared to healthy blood donors (median 5.75 mIU/ml, range: 0.1-19.5 mIU/ml) but not different from the group of renal allograft recipients without PTE (median 13.0, range 0.1-71.7 mIU/ml). However, EPO level measured in pretransplantsera was significantly highe rin patients who developed PTE(median 16.4mIU/ml, range: 1.0-281.2mIU/ml) than in recipients without PTE (median 8.3, range: 1.0-50.3 mIU/ml). A significant difference in EPO level between systemic and effluent blood from native kidneys was found in 6 out of 14 recipients with PTE who underwent catheterization. After phlebotomy patients with PTE responded with higher increase in peak EPO titer than healthy blood donors (527:t473% versus I94.5:t44.2%, p

Keywords: Kidney Transplantation, Erythropoietin, erythrocytosis