We hypothesised that 4 weeks of recombinant human erythropoietin (RhEPO) treatment would result in a significant increase in haemoglobin concentration ([Hb]) and arterial blood O₂ carrying capacity and that this would 1) increase peak pulmonary oxygen uptake (VO₂) during ramp incremental exercise and 2) speed VO₂ kinetics during 'severe', but not 'moderate' or 'heavy' intensity, step exercise. Fifteen subjects (mean ± S.D. age 25 ± 4 years) were randomly assigned to either an experimental group which received a weekly subcutaneous injection of RhEPO (150 IUkg^-1; n = 8), or a control group (CON) which received a weekly subcutaneous injection of sterile saline (10 ml; n = 7) as a placebo, for four weeks. The subjects and the principal researchers were both blind with respect to the group assignment. Before and after the intervention period, all subjects completed a ramp test for determination of the gas exchange threshold (GET) and VO₂ peak, and a number of identical 'step' transitions from 'unloaded' cycling to work rates requiring 80 % GET (moderate), 70 % of the difference between the GET and VO₂ peak (heavy), and 105 % VO₂ peak (severe) as determined from the initial ramp test. Pulmonary gas exchange was measured breath-by-breath. There were no significant differences between the RhEPO and CON groups for any of the measurements of interest ([Hb], VO₂ peak, VO₂ kinetics) before the intervention. Four weeks of RhEPO treatment resulted in a 7 % increase both in [Hb] (from 15.8 ± 1.0 to 16.9 ± 0.7 gdL^-1; P<0.01) and VO₂ peak (from 47.5 ± 4.2 to 50.8 ± 10.7 mLkg^-1min^-1; P<0.05) with no significant change in CON. RhEPO had no significant effect on VO₂ kinetics for moderate (Phase II time constant, from 28 ± 8 to 28 ± 7 s), heavy (from 37 ± 12 to 35 ± 11 s), or severe (from 33 ± 15 to 35 ± 15 s) step exercise. Our results indicate that enhancing blood O₂ carrying capacity and thus the potential for muscle O₂ delivery with RhEPO treatment enhanced the VO₂ peak but did not influence VO₂ kinetics, suggesting that the latter is principally regulated by intra-cellular (metabolic) factors, even during exercise where the VO2 requirement is greater than the VO₂ peak, at least in young subjects performing upright cycle exercise.