The effects of subcutaneous injections of human erythropoietin (rhEpo) on the circulatory response to submaximal and maximal exercise were studied in healthy male subjects (n=15). Hemoglobin concentration [Hb] increased from 152 g · l−1 to 169 g · l−1 and in parallel maximal aerobic power (Vo2max) increased from 4.52 to 4.88 l · min−1. There were no significant changes in heart rate, ventilation and blood lactate concentration during the exhausting run. Compared with infusion of red blood cells, there was no significant difference in the increase in Vo2max per gram increase in [Hb]. Systolic blood pressure at 200 W increased from before rhEpo treatment to afterwards. It was concluded that slow (rhEpo treatment) and acute (red blood cell reinfusion) increase of [Hb] resulted in similar increase in Vo2max.