The authors have demonstrated the statistically significant decrease of aldolase and pyruvate kinase activity in erythrocytes in a group of men with hypogonadism and with a significant defect of gonad endocrinologic function. A similar phenomenon appeared in erythrocytes in a group of sexually mature rabbits after castration. In the course of substitutional treatment with testosterone esters given intramuscularly, the increase of activity characteristic for both examined glycolytic enzymes was observed in both experimental groups, i.e. the patients and the animals. The pyruvate kinase increase, however, was not statistically significant in the examined group of men, which resulted from the small size of the group. The authors suggest the existence of testosterone influence on regular activity of bone marrow glycolytic enzymes, and consequently on the mature erythrocytes. The decrease of aldolase and pyruvate kinase activity in erythrocytes of patients with male hypogonadism may decrease the erythrocytes valence. This ist another biochemical argument for the need of conducting long-term substitutional therapy in cases of male hypogonadism.