Daily s.c. injection of (-)deprenyl (2.0 mg/kg/day) for three weeks in young male rats caused a threefold increase in superoxide dismutase (SOD) activity in the striatum of the brain compared with the value in saline-injected control rats. Furthermore, the activity of catalase (but not of glutathione peroxidase) was also increased significantly by deprenyl treatment. The results confirmed the previous findings of Knoll on SOD activity and furthermore provided evidence that the activity of catalase is also significantly induced by the drug, which was not found in the previous study.