Characteristics of venous flow were studied in 81 normal legs and in 98 legs with varicose vein disorders. The change in the volume in the calf after calf muscle contractions was studied using the strain gauge technique with the patients in the erect position. During contractions of the calf muscle, the volume in the calf decreases, chiefly because of reduction of blood volume in the veins. After cessation of the contractions, there is a gradual return of volume to precontraction values. This was measured in seconds and called venous return time and in milliliters times 100 milliliters of tissue-1 times minutes-1 and called venous reflux flow. In normal persons, the venous return time was 21.9+/-6.7 (S.D.) seconds, and in patients with venous disorders, the corresponding time was 6.9+/-2.9 (S.D.) seconds. Venous reflux flow which was inversely correlated with the venous return time was 11.4+/-4.9 and 22.3+/-7.3 (S.D.), respectively. A good correlation was found between venous return time and venous pressure measurements. No age or sex differences were seen. In patients with superficial venous insufficiency, the venous return time and venous reflux time became normal when the diseased portion of the vein was compressed. In patients with insufficient perforating veins or damaged deep vein valves, external compression did not change venous flow characteristics. This indicates that the method can be used preoperatively to differentiate between primary and secondary varicose veins and, thus, influence the type of operation to be performed. The method can easily be applied for clinical purposes.