Strain-gauge plethysmography was employed to quantitate the relative contributions of venous outflow obstruction and venous reflux in the postphlebitic syndrome. Both limbs of 16 normal subjects and 23 patients with venous stasis disease were studied. There were no significant differences in the mean maximum venous outflow or incremental volume values in the normal controls and patients, respectively. However, only two (6%) normal limbs had outflow values less than the lower normal limit of 25 ml/min/100 ml while 13 (33%) diseased limbs had outflows below this value. There were highly significant differences in the maximum venous reflux flow and reflux volume between controls and patients. Straingauge plethysmography may become a valuable noninvasive technique to aid in the diagnostic and therapeutic assessment of venous pathophysiology in patients with the postphlebitic syndrome.