Long-term administration of the monoamine oxidase inhibitor (-)-deprenyl (0.5 mg/Kg) for up to 20 months significantly increased mortality in the male Wistar rat, whereas the dopamine agonist pergolide (0.4 mg/Kg) and the antioxidant diethyldithiocarbamate (400 mg/Kg) had no significant effect on mortality. The increased mortality was not related to dietary intake or body weight of the rats. This is of interest in the light of recent evidence that (-)-deprenyl increases mortality in humans.