Vitamin C (ascorbic acid) is an important hydrophilic compound with antioxidative effect. In the introduction the authors describe possible consequences of loss of vitamin C synthetic ability in an evolutionary ancestor of Anthropoidea. Metabolism of this vitamin is described briefly along with possibilities of its supplementation and determination in biological fluids. Highest attention is payed to metabolic effects of vitamin C, respectively to changes which can be observed after its deprivation, or after the supplementation with this vitamin. Protective effect of vitamin C against lipoperoxidation, its role in modulation of immunity and tumorigenesis are described. Many effects of vitamin C can be explained by its antioxidative activity. The authors show that under concrete conditions, administration of vitamin C canb e accompanied by a prooxidative effect. Since vitamin C works in cooperation with other antioxidants, its administration in diseases which are followed by oxidative stress is move effective when used in combined preparations.

        Key words: vitamin C, ascorbic acid, antioxidants, lipoperoxidation.