Carbaryl was orally administered to male albino rats at 50 mg or 100 mg carbaryl/kg body weight 5 d/w for 90 d. A significant decrease in weight gain was observed at the high dosage after 60 d. Although no significant changes in the weight of testes, epididymides and accessory sex organs occurred, moderate to marked histopathological changes in the testes were seen at both dosage levels. Testicular enzymes associated with post-meiotic spermatogenic cells (sorbitol dehydrogenase) decreased, while lactate dehydrogenase increased concomitant with the observed degeneration of spermatogenic cells. Enzymes associated with pre-meiotic spermatogenic cells or Sertoli cells (gamma-glutamyl transpeptidase) increased, while glucose-6-phosphate dehydrogenase decreased. These effects were dose related and associated with declines in epididymal sperm count and percent sperm motility and increased abnormal sperm morphology.