We have examined the hormonal alterations of testicular function in 27 males (14 to 67 years of age) with soft-tissue sarcoma who were treated with surgery and high-dose radiation to the tumor bed. The testicular dose from scatter radiation ranged from 1 to 2,500 rad. There was a dose-dependent increase in the median per patient difference from baseline in serum follicle-stimulating hormone (FSH) values following irradiation, with the maximal difference seen at 6 months. Recovery of serum FSH level was biphasic with a decline in the median difference in values between 6 and 12 months, followed by a gradual descent toward baseline. Only patients receiving less than 50 rad show early complete recovery 12 months after radiation therapy. Radiation injury also induced dose-dependent increases in serum luteinizing hormone (LH) concentration, with the maximal median difference from baseline level occurring at 6 months. Only those patients receiving greater than 200 rad showed statistically significant LH changes from baseline levels at each time interval up to 30 months. No significant changes were observed in total testosterone values. These data provide quantitative guidelines for predicting seminiferous tubule injury and germ cell depletion in men exposed to fractionated radiation. The effects on seminiferous tubule and Leydig cell function, as judged by serum FSH and LH concentrations, suggest that subtle Leydig cell dysfunction, in addition to germ cell depletion, may also occur at exposures greater than 200 rad.