We studied 19 Ugandan boys with Hodgkin's disease who had been treated with mechlorethamine, vincristine, procarbazine and prednisone and who survived at least two years to assess testicular germ-cell depletion in pubescent boys on combination chemotherapy, as had previously been demonstrated in sexually mature men. Nine of 13 pubertal boys (ages 11 to 16) had moderate to severe gynecomastia and germinal aplasia, a 10-fold increase in mean (+/- S.D.) serum follicle-stimulating hormone (34.8 +/- 20.5 mlU per milliliter), a threefold increase in mean luteinizing hormone (17.8 +/- 9.8 mlU per milliliter) and reduced serum testosterone levels. Gynecomastia was not associated with an increase in either serum estradiol or prolactin concentrations. By contrast, six prepubertal boys (three to 10 years of age), similarly treated, showed no change in serum gonadotropins, and gynecomastia did not develop. The data confirm germ-cell depletion after combination chemotherapy and indicate further that Leydig-cell dysfunction, manifested by gynecomastia, may be a consequence of treatment in adolescent boys.