Testicular function was studied in 26 men with sarcoma who received adjuvant treatment with doxorubicin, cyclophosphamide, and high-dose methotrexate (with or without radiotherapy). Testicular size, sperm output, and serum FSH, LH and testosterone levels were assessed after treatment. Five of 17 men who received chemotherapy or chemotherapy with radiotherapy to the neck, arm, chest, or leg, had normal testicular function. Eight of the remaining 12 men who provided ejaculates were oligospermic or azoospermic and serum FSH was increased threefold and LH twofold; testosterone levels were normal. In the five men with normal testicular function, FSH was increased fourfold during therapy but returned to normal six to 21 months after treatment. In men less than 40 years old, the mean FSH was less than that of men over 40 years of age (P = to 0.05), suggesting that recovery from the injury was age-related. By contrast, all nine men who received chemotherapy plus radiotherapy to the abdomen or thigh had decreased testicular size, azoospermia, fourfold increase in FSH, and twofold increase in LH levels; but testosterone concentration was normal. These data increase in FSH, and reversible testicular injury occurs after treatment with doxorubicin, cyclophosphamide, and high-dose methotrexate; recovery is age-related. However, these agents in combination with use of adjuvant radiotherapy to the thigh or abdomen may produce permanent testicular injury even in young patients.