The duration of deep venous valvular reflux was studied in 192 venous segments of the legs of 32 patients in good health. Three methods were used to elicit reflux in the supine and upright positions—Valsalva's maneuver, proximal limb compression, and release of distal limb compression. Standardized compressions were achieved with pneumatic cuffs. When this approach was used to study valve function, the time to complete closure of the valve and cessation of retrograde flow was found to be shorter than that for conventional methods of closure. The distal cuff deflation method is the only one that permits a quantitative and reproducible method to measure duration of venous reflux at all levels of the lower limb. Normal values obtained with this test are presented for the common femoral, deep femoral, and superficial femoral veins and for the popliteal and posterior tibial veins midway between knee and ankle level and the posterior tibial vein at the ankle. In the popliteal vein, median duration of reflux is 0.19 second; 95% of the values in the popliteal vein are less than 0.66 second. In distal areas, duration of reflux is short and uniform. The advantage of the cuff deflation test over the Valsalva method is that the cuff method is not hindered by the presence of ileofemoral valves. A better understanding of the relative importance of deep valve dysfunction at different levels and the expected benefit of valve repair may be obtained with this test. (J Vasc Surg 1989;10:425–31.)