In 3-month-old Wistar rats carrageenan and CCl4 injected intraperitoneally induce an acute phase reaction which is characterized by a marked increase in alpha 1, alpha 2, beta serum globulins. This reaction corresponds to a large increase in these globulins in the first case and a smaller one in the second. A lipoperoxidant effect is demonstrated by the serum lipoprotein mobility as the lipoperoxidation index (in MDA units) or the decrease in serum vitamin A and E concentrations. This effect is also greater in the first case than in the second one. In the same way the lipoperoxidant effect is shown in liver microsomes but with a lower amplitude in the first case than in the second one. The treatment of rats by intraperitoneal injection of diosmine (150 mg/kg per week) during the 8 weeks which precede the injection of carrageenan or CCl4 results in: i) a marked decrease in the acute-phase reaction and a lower one in the lipoperoxidant effect, in serum; ii) a decrease in the CCl4 induced lipoperoxidant effect in liver microsomes. It may be concluded that diosmine, not injected at the same time as carrageenan or CCl4, but during the previous 8 weeks is sufficiently well distributed in the whole body to produce a marked inhibition of the acute phase reaction and a perceptible effect on lipoperoxidation. It may be considered an effective complement to the natural antioxidant defences of the organism (vitamins A and E).