Basal and stimulated plasma renin activity (PRA) and plasma aldosterone (PA) were measured in 13 hypertensive and 16 normotensive patients with kidney allografts one to nine years after transplantation. In both groups no significant differences were observed between mean basal and stimulated PRA and PA values. Therefore, we conclude that abnormal renin secretion might not be the main factor causing hypertension in renal allograft recipients. Other mechanisms seem to be involved in the pathogenesis of hypertension in these patients.