Effects of androgens on red blood cell (RBC) oxygen transport, RBC metabolism and work capacity in chronic hemodialysis patients were evaluated in a prospective controlled study. Compared to control subjects, patients given nandrolone decanoate had a sustained fall in RBC ATP and a transient rise in RBC DPG but P50 values were unchanged. Despite increases in RBC mass of 16–44% on androgen therapy, excercise on the treadmill improved in only 1 patient and actually declined in 3 others. Thus, these preliminary observations suggest that androgens may not improve hemoglobin-oxygen transport and that androgen-induced increases in red cell mass may only balance increased tissue oxygen requirements produced by these anabolic hormone