Clearance experiments were conducted to determine the effects of atrial natriuretic factor (ANF) on renal hemodynamics and excretory function in anesthetized, euvolemic Munich-Wistar rats. Intra-aortic infusions of synthetic ANF (28 amino acids) at 7.5 and 15 micrograms X kg-1 X h-1 produced dose-related increases in absolute and fractional sodium and water excretion under steady-state conditions; renal blood flow (RBF) was unchanged, whereas mean arterial pressure significantly decreased but remained within the autoregulatory range. An apparent maximal response was elicited by 15 micrograms X kg-1 X h-1 as 30 micrograms X kg-1 X h-1 produced a similar increase in urine flow and sodium excretion. ANF infusion at 30 micrograms X kg-1 X h-1 produced no transient or sustained changes in RBF (electromagnetic flow probe). Renal vascular resistance was significantly decreased in parallel with reductions in arterial pressure; ANF-induced changes in resistance can be explained by autoregulatory adjustments. In another series, intra-aortic vs. intravenous infusion of ANF (7.5 micrograms X kg-1 X h-1) were compared in the same animal; the diuretic and natriuretic response to ANF was similar with the two routes of administration. We observed no consistent changes in glomerular filtration rate (GFR). Our results indicate that the diuretic and natriuretic effects of synthetic ANF in the rat do not require an increase in RBF or GFR.