[en] The generation of free radical species as a result of radiation exposure is a well-known process. Protection against oxidative damage is possible by endogenous antioxidant defense (enzymatic and nonenzymatic components) but also by drug and dietary treatment. Among the enzymes, glutathione peroxidase (GSH-Px), copper-zinc-containing superoxide dismutase (CuZn SOD), manganese-containing superoxide dismutase (Mn SOD) and catalase (CAT) form the primary intracellular defense system. Nonenzymatic components which regulate autoxidative defense are: glutathione and other sulfhydryl, metals, metalloproteins and antioxidant vitamins. Selenium as a constituent of glutathione peroxidase (GSH-Px) and selenium-containing proteins play an important role in radiosensitivity of the cells. Changes in nutritional Se status would alter the cellular Se concentration, which in turn would result in the loss or restoration of GSH-PX activity. Although it is now evident that a decrease of the selenium and GSH-PX levels can cause radiosensitization, it is less clear whether an increased level can afford radioprotection. Thus, the aim of this work was to study the effect of selenious yeast ingestion on the Se contents in blood, hair, and feces of rats and its effect on radiosensitivity. 3 refs., 1 fig., 3 tabs