Sodium reabsorption in the kidney should be as closely related to ATP synthesis as it is to oxygen consumption. This problem was investigated in the present studies with the assumption that the uptake of inorganic phosphate by ATP is related to the rate of ATP synthesis. Radiophosphate was infused into anesthetized dogs in the course of renal clearance studies. The experimental protocols included the administration of compounds known to affect sodium reabsorption or renal cortical metabolism. At the termination of the function study, the renal cortices were removed and their nucleotides separated by column chromatography. The specific activity of ATP and sodium reabsorption in control studies were compared to values obtained in experimental studies. Sodium reabsorption was reduced with and without an effect on the specific activity of ATP. Conversely, ATP specific activity was reduced with and without an effect on sodium reabsorption. We conclude that a part of cortical sodium reabsorption can be energized other than by ATP metabolism.