Neuropeptide Y (NPY) is a potent vasoconstrictor peptide contained in sympathetic nerve terminals and is co-released with norepinephrine. Previous studies in the rat have suggested that NPY influences renal sodium reabsorption and renin release. However, little is known about the physiological effects of NPY on the kidney in the human. In the present study NPY was infused intravenously and directly into the renal artery of the primate Macaca fascicularis, an experimental model of the human. Intravenous NPY infusion at doses of 20-1,000 ng.kg-1.min-1 produced dose-dependent rises in renal vascular resistance with minimal changes in arterial pressure. Urine flow and sodium excretion were changed significantly only at doses of NPY that significantly reduced renal blood flow and filtration rate. Arterial plasma renin activity and renin secretion rate were not significantly altered at any dose of NPY. Intrarenal infusion of NPY at doses of 20-400 ng.kg-1.min-1 produced potent dose-dependent renal vasoconstriction with minimal changes in arterial pressure. Under these conditions sodium excretion was significantly reduced concurrent with decreases in renal blood flow and glomerular filtration rate. However, no significant changes in arterial plasma renin activity or renin secretion rate were found at any dose of NPY. These data indicate that in the nonhuman primate NPY is a potent renal vasoconstrictor agent that has variable effects on renal excretory and secretory function, which may be secondary to its vasoconstrictor actions.