Adult Sprague-Dawley male rats (65 days of age) received 10 daily treatments of 0, 200 or 400 mg benomyl/kg/day by gavage. Body weight, tissue weights, total epididymal sperm counts and sperm concentration from the vas deferens were measured 14 days after the last treatment. Testicular histology was evaluated in the 0 and 400 mg/kg/day groups. Significant findings included 35-48% depressions in the total epididymal sperm counts and in the vas deferens sperm concentrations in adult animals treated with 200 or 400 mg/kg/day. Histological evaluations of testicular sections from 6 adult animals in the 400 mg/kg/day group indicated a slight to moderately severe hypospermatocytogenesis in 2 animals and a slight to severe generalized hypospermatogenesis in 2 animals. Caudal epididymis weights were significantly (P less than 0.05) depressed with benomyl treatment. No treatment effects were found in body weight, liver, kidney, tests, or seminal vesicle weights.