The lymphagogue activity of a micronized, purified flavonoidic fraction, Daflon 500 mg (D) (diosmin 90%+ hesperidin 10%) was tested in dogs and rats. METHODS In the anaesthetized mongrel dog measurement of lymphatic flow was carried out in a thoracic duct fistula inserted 30 min prior to I.V. injection of D (3.125; 6.250 and 12.500 mg/kg-1). Lymph was collected every 10 min for 200 min. Using the same experimental model 14C-diosmin transfer from blood to lymph was studied after I.V. infusion (5 min) of 14C-diosmin (50 muCi)+D(12.5 mg/kg-1) in the saphenous vein. Similar experiments were performed in the rat after oral treatment. RESULTS D induced an important lymphatic flow increase which was correlated with the administered doses. The maximal 10 min period flow after I.V. injection of D (12.500 mg/kg-1) was 191% higher than the corresponding one in the control group. A correlation between lymphatic flow increase and pulsatility was demonstrated. Infusion of 14C-labelled-D evidenced a clear blood-lymph transfer of the drug: an active transport into the lymph was suggested during a 15 min-100 min period from the concentration curves. CONCLUSIONS The improvement of lymphatic drainage displayed by D seems to be an important component of its beneficial effect on perivascular edema.