The influence of UV-B radiation on superoxide dismutase (SOD, EC 1.15.1.1) with reference to the activity and types of isoenzymes was studied in leaves of C3plants (potato,Solanum tuberosumL. cv. Désirée, and wheat,Triticum aestivumL. var. Almansor) and C4plants (maize,Zea maysL. var. LG12, and sorghum,SorghumPr 8515 Pioneer). Plants were grown under controlled conditions in growth chambers with and without UV-B radiation. After 10 days of irradiation it was found that UV-B affected both the total activity of SOD and the number and amount of isoforms in all plants. The total specific activity of SOD increased significantly in wheat, maize, and potato, whereas a decline was induced in sorghum. Native gels revealed that UV-B caused preferential changes of the SOD isoforms in all plants used. Inhibition studies with cyanide and hydrogen peroxide showed that, in maize, UV-B radiation caused a large accumulation of one Mn-SOD and in contrast the level of the Cu,Zn-SOD isoforms decreased. In potato leaves, UV-B changed the pattern of SOD isoenzymes causing the appearance of one isoform and the disappearance of another. In wheat and sorghum the pattern of the isoenzymes was not altered, only their relative amounts. The rise in SOD activity in maize, potato, and wheat is possibly correlated with the tolerance of UV-B ascribed to these crops by different researchers and the sensitivity of sorghum to UV-B is possibly associated with the decrease in SOD activity.Key words: superoxide dismutase, UV-B, maize, potato, sorghum, whea