Sperm counts were low (median, 15 X 10(6) per ejaculate) and serum follicle-stimulating hormone (FSH) levels were moderately elevated (median, 31 IU/l) after unilateral orchiectomy and immediately before radiotherapy and chemotherapy in 34 patients with seminomas and 20 patients with nonseminomatous germ cell tumors. The scattered radiation (0.2 to 1.3 Gray [Gy]) reaching the remaining testicle during radiotherapy caused azoospermia in more than two thirds of the patients. A median of 540 days elapsed after the end of treatment before spermatozoa were again found in semen samples, while a median of 1250 days passed before the pretreatment sperm count was reached. One to 5 years after treatment, sperm counts were still low (median, 6 X 10(6) per ejaculate) and serum FSH was elevated (median, 61 IU/l). The adjuvant chemotherapy given to the 20 patients with nonseminomatous tumors did not appear to affect restitution appreciably.