Abstract—The N-methyl-D-aspartate (NMDA) subtype of the ionotropic glutamate receptor is found in the periphery. The present study tested whether NMDA receptors (NMDARs) are present in the ends of afferent renal nerves in the renal pelvis, an area concerned mainly with transmitting sensation and the to reflex regulation of body fluid. The main NMDAR subunit, NMDA1, was found to be more abundant in the renal pelvis than the renal cortex and medulla, and was mainly colocalized with the pan-neuronal marker PGP9.5 or the sensory nerve marker, the neurokinin-1 receptor. However, NMDA1 mRNA was undetectable, suggesting that it might be synthesized outside the renal pelvis. Intrarenal arterial administration of the specific ion channel blocker (+)-MK-801, but not the inactive enantiomer (-)-MK-801, decreased urine output and sodium excretion. High doses of (+)-MK-801 also caused regional vasoconstriction in the renal cortex, as determined by laser-Doppler flowmetry. Intrapelvic administration of the NMDAR ligand D-serine caused a dose-dependent increase in substance P (SP) release and afferent renal nerve activity, but had no effect on arterial pressure. The D-serine–induced sensory activation and SP release were abrogated by (+)-MK-801, the SP receptor blocker L-703,606, or dorsal rhizotomy. Increasing intrapelvic pressure resulted in an increase in afferent renal nerve activity and a diuretic/natriuretic response. Interestingly, these effects were attenuated by prior administration of (+)-MK-801. These results indicate that NMDAR-positive sensory nerves are present in the renal pelvis and contribute to the renorenal reflex control of body fluid.