In 21 rabbits bilateral renal artery stenosis was produced by constriction of the right renal artery with 1 of 3 different clips in size followed by left renal artery constriction with the smallest clip. Five to 6 weeks after left renal artery constriction, 5 ml. of the blood samples for the measurement of plasma renin activity (PRA) was taken from both renal veins and the distal vena cava, and the left nephrectomy was performed. In 17 out of 21 rabbits, PRA was determined in 3 different blood veins: L, left renal vein PRA; R, right renal vein PRA; and P, distal vena cava vein PRA. Three PRA patterns, L greater than P greater than or equal to R (A type), L, R greater than P (B type) and R greater than L not equal to P (C type), were observed. Removal of the left kidney caused a significant decrease in the average blood pressure persisting for 5 weeks in the rabbits with the type A pattern of PRA (p less than 0.05). In all 4 animals with the type B or C pattern of PRA hypertension persisted even after removal of the left kidney. Comparison of the PRA values between the venous blood in 3 different vascular trees seems very useful to predict the depressor response that follows nephrectomy of the severer constricted side.