Hypertension is the most common cardiovascular complication after liver transplantation. Systemic vasoconstriction underlies transplant hypertension, but the mechanisms contributing to this remain unresolved. Plasma renin, aldosterone, and endothelin (ET)-1 together with augmentation index, a measure of arterial stiffness, were determined before and at intervals of 1, 3, and 6 months after transplant in 32 consecutive patients accepted for liver transplantation. At 3 months, 47% of patients were hypertensive, and at 6 months, 50% of patients were hypertensive. Plasma renin and aldosterone decreased after transplantation but were no different between hypertensive and normotensive patients. Plasma ET-1 levels were elevated pretransplant and decreased at 1 month, but at 6 months, levels were elevated in hypertensive patients but not in normotensive patients (P=0.019). Augmentation index increased after transplant and was greater in the hypertensive patients compared with the normotensive patients (P=0.031). During the first 6 months, the renin-aldosterone system does not play a significant role in posttransplant hypertension. Elevation in plasma ET-1 and increases in arterial stiffness are potential important mechanisms underlying the development of hypertension after liver transplant.