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Pavlata L., A. Pechova, J. Illek: Direct and Indirect Assessment of Selenium Status in Cattle - a Comparison. Acta vet. Brno 2000, 69: 281-287. Selenium concentration and activity of glutathione peroxidase (GSH-Px) as direct and indirect indicators of selenium status were determined in whole blood samples collected from 326 cattle in 30 herds kept in various regions of the Czech Republic. The GSH-Px activity in the samples was measured by the UV method, using the set supplied by Randox. Selenium in the sample was measured using the hydride technique AAS. The two variables showed a close and significant correlation (r = 0.90; p < 0.01). The regression line, defined by the equation y = 6.44x + 21.4, allowed us to determine the GSH-Px activity of 665.4 µkat.l -1 as equivalent to selenium concentration in whole blood 100 µg.l-1 . Mean selenium concentration and mean GSH-Px activity found in whole blood samples were 78.25 ± 46.67 µg.l-1 and 525.51 ± 335.56 µkat.l-1, respectively. Insufficient or marginal supply of selenium was diagnosed in 64% of the animals in terms of selenium concentration, in 63% of the animals in terms of GSH-Px activity and in 55% of the animals with selenium concentrations <100 µg.l -1 and GSH-Px activity < 665.4 µkat.l -1 . In this study, close dependence of GSH-Px activity and selenium concentration in the blood of cattle was found. Activity values of GSH-Px were determined for the use in diagnosis of insufficient selenium in cattle in the Czech Republic.