The effect of amino acid infusion on renal hemodynamics was examined in 13 healthy subjects. Seven subjects participated in the first experimental protocol: study 1 -amino acids were infused for 3 h to increase plasma amino acid levels 2- to 3-fold above baseline; study 2 – amino acids were infused with somatostatin and peripheral replacement of insulin, glucagon and growth hormone; and study 3 – somatostatin and hormones were infused as in study 2, but no amino acids were infused.During study 1 both glomerular filtration rate (GFR) and renal plasma flow (RPF) increased by 20%. In contrast, when amino acids were infused with somatostatin (study 2), neither GFR nor RPF changed from baseline. In study 3, somatostatin alone had no effect on GFR and RPF.In a second experimental protocol, 6 subjects were maintained for 7 days on a low protein diet (40 g/day); amino acids were infused as in study 1 before and after the protein restriction. Baseline GFR and RPF both decreased significantly after protein restriction. The response to amino acid infusion was not changed.These results indicate that: (1) hyperaminoacidemia causes a rise in both GFR and RPF; (2) the increase is likely to be mediated by some hormones whose secretion is inhibited by somatostatin, and (3) protein restriction causes a decline in GFR and RPF but fails to alter the renal hemodynamic response to amino acid infusion.