Posttransplant hypertension is an important risk factor for cardiovascular mortality and graft function. We performed metabolic studies in 35 hypertensive patients with well-maintained graft function on maintenance immunosuppressive drugs and in 17 normotensive control transplant recipients. The group of hypertensive recipients were characterized by increased peripheral plasma renin activity, lack of change in blood pressure in response to salt loading and restriction, and by increased peripheral and renal resistance. In contrast, on the same protocol in a group of patients with essential hypertension, blood pressure fell significantly on a low-salt intake. Peripheral resistance in hypertensive transplant recipients fell in response to saline loading, in contrast to the effects in normotensive transplant recipients. Hypertensive patients with retained native kidneys as compared to those who had these removed prior to transplant, but were still hypertensive, differed only with regard to reduced renal plasma flow in the former group. These data are consistent with a predominantly renin-dependent hypertension in these renal transplant recipients. When bilateral nephrectomy or repair of graft renal artery stenosis is being considered, response to captopril may offer a means of selection; acute renal failure on captopril suggests functionally significant renal artery stenosis.