Leg volume changes during exercise have been measured in absolute units (milliliters) by means of a new method of air-plethysmography. Venous volume (VV), venous filling time, and venous filling index on standing from the recumbent position, ejected volume (EV) and ejection fraction (EF = EV x 100/VV) with one tiptoe movement, and residual volume (RV) and residual volume fraction (RVF = RV x 100/VV) after 10 tiptoe movements were measured in normal limbs, limbs with superficial venous incompetence, and limbs with deep venous disease. The same measurements were repeated with a graduated medium compression stocking in limbs with SVI and graduated high compression stockings in limbs with DVD. Ambulatory venous pressure was measured at the same time, with a needle in a vein in the foot. The results indicate that this method of air-plethysmography is not only of diagnostic value but offers a new and unique technique to assess and study the hemodynamic effects of different forms of elastic compression. The lower ambulatory venous pressure, produced by the elastic compression, was the result of a reduction in reflux and an improvement in the calf muscle ejecting ability during rhythmic exercise.