After intravenous administration of alloxan monohydrate (AL) diabetes developed in rats. Forty-eight hours after the injection the animals were sacrificed, their blood was collected in heparin containing tubes and the tissues were dissected and frozen (-70 degrees C) until their homogenization for pro- and antioxidant testing. Our results can be summarised as follows: (i) In the blood hemolysate the lipid peroxidation slightly elevated and the activity of antioxidant enzymes and reduced glutathione decreased. (ii) Similar phenomena could be observed in the different examined organ homogenates. The organs tested for pro- and antioxidant system were as follows: the liver, heart, skeletal muscle, kidney and pancreas. In our present work we attempt to confirm the data in support of the oxidative predominance over antioxidants in oxidative stress of AL diabetic rats.