In order to investigate the role of circulating humoral substances in the pathogenesis of venous changes in experimental hypertension, an attempt was made to induce venous changes in rats in parabiosis with two-kidney Goldblatt hypertensive rats. Sham-operated normotensive rats in parabiosis were used as controls. Venous pressure-volume curves were obtained in the pump perfused vascular beds of the lower body of rats by recording the femoral vein pressure rise during rapid infusion of fluid into the inferior vena cava. The water, sodium and potassium content of veins also was measured. Compared to values in normotensive control rats (n = 11), the venous pressure-volume curves of two-kidney Goldblatt hypertensive rats in parabiosis with unoperated rats (n = 13) were shifted in the direction of the pressure axis (p < 0.01), indicating decreased venous capacity. Venous pressure-volume curves in rats in parabiosis with two-kidney Goldblatt hypertensive rats (n = 13) and in rats in parabiosis with sham-operated rats (n = 10) were similar. The venous wall water, sodium and potassium content in two-kidney Goldblatt hypertensive rats (n = 8) and in their unoperated parabiotic mates (n = 8) was increased (p < 0.05) in comparison to that of sham-operated rats in parabiosis (n = 10). These experiments provide evidence for the role of circulating humoral substances in the pathogenesis of abnormal venous wall composition but not of decreased venous capacity in renal hypertensive rats.