Each step of an inflammatory reaction is triggered by one or several chemical or biological mediators such as arachidonic acid derivatives (prostaglandins [PG], leukotrienes [LT], or thromboxanes [TX]), vasoactive amines (histamine or serotonin), and oxygen free radicals (superoxide ion, O2-, or hydrogen peroxide, H2O2). In perivenous inflammation, these mediators play a prominent role in favoring vasodilatation (histamine), increasing membrane permeability (PGE2, histamine, free radicals) and providing a chemotactic signal for specialized cells, ie, neutrophil polynuclears, macrophages, lymphocytes (LTB4, free radicals). The antiinflammatory effects of Daflon 500 mg,* a micronized purified flavonoid fraction (90% diosmin, 10% hesperidin), were studied in different in vivo and in vitro models. In a model of inflammatory granuloma in the rat, Daflon 500 mg (100 mg/kg, orally) reduced edema formation and inhibited the synthesis for PGE2 (78.5%), PGF2 alpha (45.2%) and TXB2 (59.5%) (Damon et al, Arzneim-Forsch/Drug Res 37:1149-1153, 1987). Intravenous injection of Daflon 500 mg (25 and 50 mg/kg) reduced the hyperglycemia induced by injection of alloxan in rat. This effect of Daflon 500 mg was linked to its ability to scavenge active oxygen radicals, demonstrated in vitro using human neutrophils (Lonchampt et al, Arzneim-forsch/Drug Res 39:882-885, 1989) or mouse peritoneal macrophages (Bodinier et al, manuscript in preparation) stimulated by zymosan. The free radical scavenger effect of Daflon 500 mg is observed at concentrations ranging from 10(-7) M to 10(-4) M, with half-maximal effect between 10(-6) M and 10(-5) M. Thus, Daflon 500 mg behaves as a potent protective agent against inflammatory disorders. These properties may explain, at least in part, the clinical activity of Daflon 500 mg and justify its therapeutic use.