Experiments were designed to evaluate the influence of the renal efferent nerves on baseline renal function and on the renal response to atrial natriuretic factor (ANF) in euvolemic anesthetized 10- to 12-wk-old spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) and Munich-Wistar (MW) rats. Acute unilateral renal denervation produced increases in absolute and fractional excretion of sodium and water by the ipsilateral kidney that were similar in SHR and WKY rats; larger responses were observed in MW rats. Excretion by the contralateral innervated kidney was unchanged in each group. Intravenous infusion of ANF (0.25 μg·kg-1·min-1) caused a diuresis and natriuresis that was similar in the three strains and independent of changes in glomerular filtration rate and renal blood flow. The excretory responses to ANF were larger in denervated than in innervated kidneys. The magnitude of the natriuresis and diuresis produced by ANF was directly related to the pre-ANF rate of urinary excretion, suggesting independent and additive effects of acute renal denervation and ANF on tubular reabsorption. The exaggerated response in the acutely denervated kidney can be explained by removal of a modulatory effect of the renal efferent nerves and associated increases in tubular flow and delivery to more distal ANF sensitive sites. The denervation responses suggest that the renal efferent nerves have similar effects on sodium and water reabsorption in anesthetized SHR and WKY rats at 10-12 wk of age. The renal nerves and ANF appear to play a larger role in the acute control of sodium and water excretion in MW rats compared to rats of the Okamoto-Aoki strain.