We studied the effects of unilateral lumbar sympathetic block on kidney function in eight patients with cirrhosis and hepatorenal syndrome. In five patients with basal glomerular filtration rate (GFR) below 25 ml/min, sympathetic block induced a significant increase in GFR, osmolal clearance, urinary sodium excretion, fractional excretion of filtered sodium (FENa) and effective renal plasma flow (ERPF) and a decrease in plasma renin activity. In the three patients with basal GFR greater than 25 ml/min, sympathetic block produced no significant change in renal function. We conclude that sympathetic block might improve renal function in cirrhotics with hepatorenal syndrome, particularly those with more impaired GFR.