Abstract. The aim of this study was to characterise the effect of prolonged low doses of recombinant erythropoietin (r-HuEPO) on the responses to submaximal and maximal exercise. Volunteer recreational athletes (n=21) were divided into three groups: r-HuEPO+intravenous iron (EPO+IV, n=7), r-HuEPO+oral iron (EPO+OR, n=9) and placebo (n=5). During the 12week study, r-HuEPO or saline injections were given three times a week for the first 8weeks and for the final 4weeks the subjects were monitored but no injections were administered. The r-HuEPO doses were 50IUkg1 body mass for 3weeks and 20IUkg1 body mass for the next 5weeks. An exercise test comprising three submaximal intensities and then increments to elicit maximal aerobic power ( ) was conducted during weeks0, 4, 8 and 12. During week0, the mean intensity of the submaximal stages was 60%, 72% and 81% . Blood taken at rest was analysed twice a week for haematocrit (Hct). The relative increases in at weeks4, 8 and 12 were 7.7%, 9.7% and 4.5%, respectively, for the EPO+IV group; 6.0%, 4.7% and 3.1% for the EPO+OR group; and 0.5%, 0.1% and 1.0% for the placebo group, where the improvements at week12 for the EPO+IV and EPO+OR groups remained significantly above week0 values. The Hct was significantly elevated by 0.06 and 0.07 units at week3 in the EPO+IV and EPO+OR groups, respectively, and was stable during the 5weeks of low-dose r-HuEPO. After 8weeks of r-HuEPO use, plasma lactate concentration tended to be lower at exercise intensities ranging from 60% to 100% . This study confirmed the ability of low doses of r-HuEPO to maintain Hct and at elevated levels.