Androgenic steroids have been shown to enhance erythrocyte 2,3-DPG production in vivo and in vitro, and to stimulate the pentose shunt oxidative reactions in vitro. Furthermore, a 3 beta- and a 17 beta-hydroxysteroid dehydrogenase have been identified in red cells. The present study was carried out to explore a cumulative effect of androgens on glycolysis and androgen reduction in human erythrocytes in vivo following a single 50 mg oral dose of 17 beta-hydroxy-2 (hydroxymethylene)-17 methyl-5 alpha-androstan-3-one (oxymetholone). The rate of erythrocyte glycolysis was measured by quantitative determination of: fructose-1,6-diphosphate (FDP); dehydroxyacetone phosphate (DAP); 2,3-diphosphoglycerate (2,3-DPG); adenosine triphosphate (ATP); and lactate. Serum and erythrocyte steroids were separated by thin layer chromatography. The reduction of 5 alpha-androstan-17 beta-ol-3-one by red cell hemolysate was measured in the presence of NADPH as an index of 3(17)beta-hydroxysteroid dehydrogenase activity. Our results show that oxymetholone administration is followed by the appearance of an unidentified steroid fraction in chromatograms of serum and erythrocytes, simultaneously with the enhancement of glycolysis and of hydroxysteroid dehydrogenase activity in erythrocytes. A direct effect of androgen on erythrocyte metabolism, which is independent of the hormone erythropoietic effect, is discussed.