Acute intravenous amino acid infusion or a high-protein diet increases renal plasma flow and the glomerular filtration rate in healthy subjects. Conversely, a low-protein diet reduces renal plasma flow and glomerular filtration rate. The aim of this study was to investigate the effect of intravenous amino acid infusion and dietary proteins on kidney function in cirrhosis. Protocol 1: renal plasma flow and glomerular filtration rate were measured before and during intravenous administration of a 10% amino acid solution (0.043 ml/kg/min) to eight compensated cirrhotic patients (group 1), nine nonazotemic cirrhotic patients with ascites (group 2) and seven cirrhotic patients with ascites and functional renal failure (group 3). Amino acid administration induced a significant increase in renal plasma flow and glomerular filtration rate in all groups studied. Renal plasma flow and glomerular filtration rate increased by 16% and 14%, respectively, in group 1; 31% and 22% in group 2 and 25% and 21% in group 3. Protocol 2: Renal plasma flow and glomerular filtration rate were measured in nine cirrhotic patients with ascites after 11 days on a low-protein diet (0.5 gm/kg body weight/day) and also after the patients followed for 11 days a moderately high-protein diet (1.5 gm/kg body weight/day). The moderately high-protein diet was associated with a significant increase in renal plasma flow (12%) and glomerular filtration rate (13%) compared with values obtained while the patients followed the low-protein diet. Plasma glucagon levels increased markedly during the intravenous administration of amino acid and the intake of the moderately high-protein diet.(ABSTRACT TRUNCATED AT 250 WORDS)