The levels of chromosome mutations in hemopoietic cells of various fish from water bodies near the Noril'sk mining and smelting complex were estimated by the micronucleus test. In some cases very high frequencies of erythrocytes with micronuclei were observed in fish inhabiting highly polluted water bodies. On the whole, the number of cells with chromosome aberrations was within the limits of spontaneous mutagenesis. Marked species-specific, seasonal and local differences were found in the frequency of erythrocytes with micronuclei. The problems related to the influence of chemical pollutants on fish are discussed.