It has been demonstrated that patients predisposed to the development of varicose veins have an abnormal venous tone, and may have symptoms in the absence of obvious varicosities. It has been suggested that venotonic drugs relieve the symptoms of chronic venous insufficiency by decreasing capillary leakage and improving venous tone. The aim of this study was to determine the effect of Daflon 500 mg in patients with abnormal venous elasticity without varicose veins. Twenty-five healthy female volunteers aged 18-35 were included in the study. They presented with symptomatic varicose veins in one leg and an abnormal elastic modulus without varicosities in the opposite leg. Treatment group: 12 patients received 2 tablets of Daflon 500 mg (1000 mg/day); control group: 13 patients received no treatment. The elastic modulus K was determined using the air plethysmograph. Simultaneous measurements of calf volume changes were made in response to different venous pressures produced by a thigh pneumatic cuff. In the control group K (mean +/- sd) was 10.8 x 10(3) +/- 4.1 x 10(3) N/m2 at the beginning and 10.2 x 10(3) +/- 3.1 x 10(3) N/m2 at the end of the study (P > 0.1). In the treatment group the initial K was 10.2 x 10(3) +/- 3.9 x 10(3) N/m2 and 14.2 x 10(3) +/- 5.1 x 10(3) N/m2 at the end (P < 0.02). The results of the Wilcoxon rank sum test indicated that 4 weeks' therapy with Daflon 500 mg is effective in improving venous tone in patients with symptoms but without varicose veins.