To examine the effects of increasing dietary sodium intake on natriuresis, filtration rate, and renal blood flow following rapid volume expansion, we infused 2-liter normal saline over 2 hr into normal men in balance at 10, 300, 600, and 800 mEq/day sodium intake. Natriuresis and kaliuresis were related to prior sodium intake. Fractional excretion of sodium (6%-7%) was maximal at the 600 mEq/day sodium intake and increased no further at the 800 mEq/day sodium intake. Although blood pressure increased with rapid saline infusion, natriuresis and blood pressure were not associated. Creatinine clearance decreased or remained constant, while PAH clearance decreased during saline infusion at each level. The data suggest that although natriuresis following rapid saline infusion is dependent upon prior sodium intake, under given circumstances it may be independent of glomerular filtration rate, renal blood flow, or blood pressure.