Peroxidation processes in blood, liver and gills increased in the carps, which have been exposed to water environment with increased lead ion concentrations. The same effect was observed in blood and liver under influence of copper ions. Such changes are connected with decreased activities of antioxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase). Zinc ions increased the enzyme activities studied, and consequently, the malonic dialdehyde content in liver and gills decreases.