The origins of the renal efferent and afferent nerves in 5 cynomolgus monkeys (Macaca fascicularis) were studied by using the retrograde transport of horseradish peroxidase (HRP) and horseradish peroxidase-wheat germ agglutinin (HRP-WGA). The cut ends of the right renal nerves were soaked for 30-45 min in solutions consisting of 15% HRP and 1% HRP-WGA. Three or four days later the animals were killed and the tissues examined for the presence of retrogradely labeled neurons, HRP-filled cells were observed, with rare exceptions, only in ganglia ipsilateral to the side of tracer application. Renal efferent neurons (4648-14565 cells per animal) were found in relatively equal numbers in prevertebral and paravertebral (sympathetic chain) ganglia. Labeled prevertebral cells were distributed among the renal (52%), aorticorenal (32%) and superior mesenteric (16%) ganglia, whereas labeled paravertebral neurons were mainly located in chain ganglia T11-L3, with 94% of these located in L1-3. Labeled renal sensory neurons (31-543 per animal) constituted less than 5% of all labeled cells and were found in ipsilateral dorsal root ganglia T10-L3, with (80%) in T12 and L1. The labeled sensory neurons ranged from 18-64 microns in diameter (X = 32.4 microns). With the exception of a single cell in one animal, no labeled neurons were observed in the nodose ganglia. Many parallels were observed between the organization of the renal plexuses of macaques and humans, suggesting the utility of the non-human primate as an experimental model for functional studies of renal innervation in humans.