Capillary filtration (CF) was assessed in 43 patients with venous hypertension and in 10 normal subjects by means of strain gauge plethysmography. The patients were then divided into two treatment groups; 22 were treated with Daflon, 500 mg tid, and 21 with Daflon, 500 mg bid. The normal subjects were also treated (500 mg tid). After four weeks CF was significantly decreased in all subjects, the decrease being higher in the high-dose groups. CF did not significantly change in normal subjects. In conclusion Daflon decreases CF in subjects with venous hypertension and the CF decrease is dose related.