The cell-mediated immunity was studied in 14 hemodialysis patients by determination of the serum levels of soluble interleukin 2 receptor (sIL-2R) before (hemoglobin 7.9 +/- 0.6 g/dl) and after 16 months of recombinant human erythropoietin (rHuEPO) administration (hemoglobin 10.3 +/- 1.1 g/dl) and compared with 14 hemodialysis patients not receiving the drug (hemoglobin 9.7 +/- 1.4 g/dl). The sIL-2R level was higher in severely anemic patients starting rHuEPO than in patients not receiving the drug (9,414 +/- 2,822 vs. 5,001 +/- 2,905 pg/ml; p < 0.05). At the end of the 16-month observation period, a decrease in sIL-2R of about 48% was observed following raising hemoglobin with rHuEPO, whereas untreated patients exhibited a further increase in sIL-2R, amounting to 59% (p < 0.001). There was a correlation between sIL-2R and hemoglobin (r = -0.40; p < 0.02) at the start of the study and between sIL-2R and hemoglobin (r = -0.43; p < 0.02) and monocyte number (r = 0.48; p < 0.01) at the end of the observation period. Elevated serum sIL-2R levels, a characteristic finding of the altered cell-mediated immunity of hemodialysis patients, may be influenced by the increase in hemoglobin concentration following rHuEPO administration rather than by the hormone itself.