Recombinant human erythropoietin (rhEPO) was administered subcutaneously to 13 anemic (Hb < 10 g/dl) patients with myelodysplasia (MDS). rhEPO was given 3 times a week at doses of 75-250 U/kg body weight, over a maximum period of 24 weeks. Five patients (38%) showed a response to rhEPO treatment. rhEPO was well tolerated and without relevant side effects throughout the study. All responding patients had low but detectable pretreatment circulating erythroid progenitor cells (BFU-E) and the response to rhEPO was associated with a significant increase in BFU-E (p < 0.01); concentrations of serum transferrin receptor (TfR) also consistently rose in all responding patients. Baseline erythropoietin (EPO) concentrations did not significantly differ between responders and nonresponders, although 4 out of the 5 responders had relatively low levels of EPO. In conclusion, subcutaneous rhEPO administration appears to be an effective treatment of anemia in a substantial subset of patients with MDS. Relatively low baseline EPO concentrations, detectable pretreatment circulating BFU-E and an early increase in the serum concentrations of TfR seem to be criteria for predicting response to rhEPO in patients with MDS.