Abnormal increase of erythrocyte aggregation and reduction of profibrinolytic activity are the two most frequent biological perturbations found in chronic venous insufficiency (CVI). A randomised, controlled, double blind trial was undertaken on 85 patients suffering from grade 1 and 2 CVI, to compare troxerutin with placebo. Two types of biological parameters were measured after 15 days of treatment. Erythrocyte aggregation as evaluated with a Myrenne erythroaggregometer by the indices M (stasis) and M1 (3s-1) progressed favorably in the troxerutin group. The values of M1 at D15 (p < 0.05), and the progression of M (p < 0.001) and M1 (p < 0.01) from D0 to D15, are significantly better in the troxerutin group. Progression of fibrinolytic activity at rest was not significantly different between the 2 groups. Conversely, the progression from D0 to D15 of the values after occlusion of euglobulin lysis time (p < 0.01), tPA (p < 0.01), and PAI activity (p < 0.05) are significantly better in the troxerutin group. The fibrinolysis capacity estimated by euglobulin lysis time (p < 0.01) and tPA (p < 0.05) also progressed favorably in the troxerutin group. These results confirm the anti-erythrocyte aggregation effect of troxerutin, and suggest a favorable effect on blood fibrinolytic activity. They could explain the positive action of this drug on stasis, capillary perfusion and trophic complications of CVL.