Superoxide dismutase (SOD), catalase (C), peroxidase (P) and glutathione peroxidase (GSH-Px) were estimated in the erythrocytes and liver of the carp, the tench and the crucian carp during a two-years period, 1983-1984 (autumn). 2. The lipid peroxidation (LP) of the erythrocytes and liver homogenates was also compared. 3. The activities of the enzymes examined showed significant interspecies variations. 4. Significant differences were observed between enzyme activities (except for SOD in the liver) and lipid peroxidation in erythrocytes and liver of investigated fish species. 5. The very high values of peroxide enzyme activities in fish erythrocytes and SOD in fish liver suggest the predominant role of these enzymes in protection of polyunsaturated acids against uncontrolled oxidative processes.