To determine the effects of alpha-human atrial natriuretic peptide (ANP) on renal function and the renin-aldosterone system in anesthetized rabbits, ANP (0.05 micrograms/kg/min) or 5% dextrose solution in vehicle control was infused intravenously. The infusion of ANP resulted in a significant decrease in mean arterial pressure with an increase in renal blood flow (RBF). ANP also produced significant increases in urine volume and urinary sodium excretion. ANP tended to increase glomerular filtration rate, filtered sodium load and net tubular reabsorption of sodium. However, there were no significant differences in these parameters compared with control group. Fractional sodium excretion was increased significantly by ANP. Plasma renin activity (PRA) was suppressed only at 30 min after the infusion of ANP, while a significant fall in plasma aldosterone concentration (PAC) lasted even in the recovery period. These results indicate that ANP produces a diuresis and natriuresis through the increased RBF in anesthetized rabbits. It is also suggested that ANP suppresses PAC independent of the inhibition of PRA.