Systemic and renal neurovascular reactivity was investigated in eight patients with cirrhosis and in eight control subjects with fatty liver during postural changes. In the supine position, mean renal blood flow averaged 1.51 and 2.97 ml per gm per min in patients and controls, respectively (p less than 0.02). During tilting, renal blood flow changed significantly (p less than 0.05) and equally in patients and controls (15 degrees head-down tilt: 12 and 13% increase, respectively; 60 degrees head-up tilt: 27 and 32% decrease, respectively). Mean arterial blood pressure was significantly lower in patients than controls (82 vs. 95 mm Hg, p less than 0.05) but did not change during the tilt. Plasma norepinephrine (NE) concentration was significantly higher in another eight patients with cirrhosis than in eight healthy controls (mean: 0.45 vs. 0.21 ng per ml in recumbency, p less than 0.02). Following 60 degrees head-up tilt, the increase in NE was similar in both groups. In another 10 patients with cirrhosis in recumbency, the splanchnic arterial-hepatic venous extraction of NE averaged 0.43 (p less than 0.01), and the hepatic clearance of NE averaged 315 ml per min which is of the same order as previously reported in healthy controls. The right kidney released NE into the systemic circulation. Renal venous plasma NE exceeded arterial concentration by 34% (p less than 0.01). It is concluded that sympathetic nervous activity is enhanced in patients with cirrhosis, and that this hyperactivity may be responsible for renal vasoconstriction in these patients. However, systemic and renal neurovascular reactivity seems to be maintained even at an advanced stage of the disease.