We previously reported that prenatal exposure to 3,3',4,4',5-pentachlorobiphenyl (PCB126) had dose-related adverse effects on the spermatogenesis of 7(pubescent)- and 17(adult)-week-old rats, but the effects in middle and old age have been unclear. In this study, the spermatogenesis of male Sprague-Dawley rats whose dams had been injected (i.g.) with 25 pg, 2.5 ng, 250 ng, or 7.5 microg of PCB126/kg or the vehicle on days 13-19 post-conception was investigated at 52 and 90 weeks of age. At 52 weeks, the 7.5 microg group showed a significant decrease of preleptotene spermatocytes in stages VII-VIII seminiferous tubules, round spermatids increased at stages VI-VII and elongated spermatids decreased at stage VIII, while the spermatogenesis of the other PCB-treated groups were similar to that of the vehicle group. At 90 weeks, the 7.5 microg group showed a significant decrease of spermatogenic cells at many stages, and the 250 ng group showed a significant decrease of preleptotene spermatocytes at stages VII-VIII, and round spermatids increased at stages VI-VII, elongated spermatids decreased at stage VIII, and the spermatogenesis of the 2.5 ng and 25 pg groups were similar to those of the vehicle group. The present study showed that prenatal PCB126 exposure had dose-related adverse effects on spermatogenesis in aging rats and may have accelerated spermatogenic senescence. Because the serum testosterone levels of the PCB126 groups and the vehicle group were similar, a direct endocrine cause for the observed effects was unlikely.