Alloxan-induced hyperglycemia was accompanied by activation of lipid peroxidation processes with different degree of their completeness depending on the age of experimental animals. Lipid peroxidation in young animals mainly resulted in the formation of end-products, while in adult animals the initial stage of oxidation prevailed. Alloxan inhibited the enzymatic and nonenzymatic systems of antioxidant protection, which impaired adaptation and caused oxidative stress.