Twelve men with different forms and stages of chronic radiation dermatitis caused by accidental exposure to beta and gamma irradiation during and after the Chernobyl atomic power plant accident were examined. Two patients had impotentia coeundi, and the others reported various impairments of sexual function. One patient had aspermia, two patients had azoospermia, one had oligospermia, and four had normal sperm counts. In three samples abnormal forms of spermatozoa were increased. Sperm motility was decreased in 3 samples and was normal in another. Hormonal analyses demonstrated low testosterone plasma levels in two patients, an increase of follicle stimulating hormone (FSH) levels in six patients, and a decrease of luteinizing hormone (LH) in one patient. In one patient who showed an increase of plasma prolactin level, associated with low testosterone and LH, a microadenoma of the pituitary gland (prolactinoma) was detected. It would appear that there is an association between accidental exposure to ionizing radiation of varying severity and the impairment of exocrine and endocrine testicular function, sometimes resulting in long-lasting physiological and psychological problems.