The aim of this study was to evaluate the effect of hydroxyethylrutosides on capillary filtration in subjects with mild to moderate venous incompetence--superficial varicose veins and/or deep venous disease and ankle oedema--using the vacuum suction chamber (VSC) device applied to the internal perimalleolar region and the wheal vanishing (WV) time. Subjects entered in to the study were randomised to receive either hydroxyethylrutosides (1 g twice daily for 4 weeks) or placebo for four weeks. The two groups entering and completing the study were comparable. Microcirculatory parameters (laser-Doppler resting flux, the venoarteriolar response, transcutaneous PO2 and PCO2) remained constant during the four week study in both groups. The WV time, which was comparable in the two groups at the beginning of the study decreased significantly [from a median 55 min (interquartile 955 min), to a median 45 minutes (interquartile 65-40 min) in the treated group, p < 0.01]. No change was observed in the WV time in the placebo group. Subjective symptoms measured with an analogue scale improved following treatment with hydroxyethylrutosides [foot oedema (p < 0.005), ankle oedema (p < 0.001), and paraesthesia (p < 0.01)]; only night cramps were reported less in patients receiving the placebo (p < 0.05). In conclusion, the WV time can be used to assess the beneficial effect of therapy on capillary filtration in subjects with mild-moderate venous hypertension, even after a short period of treatment, and before other microcirculatory parameters change. Furthermore, the changes observed in WV time correlate well with an improvement in patients symptoms.