Mean arterial pressure, phenylalanine, tyrosine, norepinephrine and plasma renin activity (PRA) were determined in the plasma of 6 healthy controls and 8 patients with liver cirrhosis receiving a controlled sodium intake (40 mEq/day), after 1 h of bed rest and 10 min after being tilted up at 90 degrees. After resting, patients showed lower arterial pressure (p less than 0.025) and higher plasma levels of phenylalanine (p less than 0.005), tyrosine (p less than 0.05), norepinephrine (n.s.) and PRA (n.s.) than controls. In spite of a prolonged and marked stimulation of the adrenergic system induced by tilting, arterial pressure of cirrhotics, after an initial increase, decreased significantly. A significant PRA increase was observed in both groups but in patients it was greater and lasted longer, up to 30 min, when PRA and arterial pressure were inversely and significantly correlated. The adrenergic system of cirrhosis then appeared unable to maintain adequate levels of arterial pressure, even though hyperstimulated. The renin-angiotensin system played an important compensatory role in this contest.