Although many reports concerning the effects of shock waves on the human body have been published, their effects on the male reproductive system are not well known. This report examines the effects of shock waves on human spermatozoa and rat testes. Semen samples were placed in water at 37 degrees C and 100, 200, 500, and 1,000 shock waves were applied. In proportion to an increasing number of shock waves, sperm motility and the percentage of viable sperm decreased, while the percentage of short-tailed sperm increased. In a second study 500 or 1,000 shock waves were applied to the testes of infant and adult male Wistar rats. Hematomas were observed macroscopically in the testes immediately after shock wave treatment. Light microscopy showed rupture of the basement membrane of the seminiferous tubules and outflow of spermatogenic cells. After 5 weeks, the treated testes appeared atrophic, with the absence of spermatogenic cells in the seminiferous tubules, except for Sertoli cells. Our data indicate that spermatozoa and the testis appear to be structurally damaged by shock waves.