S 5682 is a purified flavonoid fraction containing 90% diosmin (flavone derivative) and 10% hesperidin (flavanone derivative). In this study the scavenging properties of S 5682 on active oxygen radicals were demonstrated in vivo and in vitro. The activity of intravenous S 5682 was evaluated in the rat by measuring the degree of hyperglycemia provoked by an intravenous injection of alloxan, the metabolism of which produces active oxygen radicals which are toxic to B cells of the pancreas. S 5682 produced a decrease in the hyperglycemia in a dose-dependent manner (25 mg/kg and 50 mg/kg). The production in vitro of active oxygen radicals during phagocytosis by polymorphonuclear cells and macrophages is accompanied by emission of photons which can be amplified in the presence of luminol. Measurement of this chemiluminescence is a way of determining the quantity of active oxygen radicals generated in the medium, this may be reduced either by a decrease in production or by an increase in neutralisation through a reducing effect. Results demonstrated that S 5682 had a scavenging effect on active oxygen radicals for concentrations between 2 x 10(-8) mol/l and 2 x 10(-4) mol/l. The concentration of S 5682 reducing the chemiluminescence by 50% was 1.6 x 10(-5) mol/l. These scavenging properties imply that S 5682 has a pharmacological action on capillary hyperpermeability as well as an anti-inflammatory and anti-oedematous action.