In 10 female and 10 male haemodialysis patients plasma FSH, LH, testosterone, prolactin, and somatotropin (STH) were estimated during erythropoietin (rHuEpo) treatment for 6 months. All but one patient responded with an increase in haemoglobin. The patients experienced improved sexual function according to the answers given in a self-administered questionnaire. Of the 90% who answered before the study 22% could not perform sexual activities whether they wanted to or not. During and at the end of the study 80 and 60% respectively answered, and none had these problems. In contrast, serum values of the sexual hormones (FSH, LH, testosterone and prolactin) were not significantly changed during rHuEpo therapy, and neither was the basal plasma STH.