Stimulating electrodes were placed on the terminal branches of the pelvic nerves to the urinary bladder and the pudendal nerve to the sphincters in seven Rhesus monkeys and two chimpanzees. The proximity of the electrodes to these structures assured organ specificity. Evoked responses produced by stimulation of these terminal nerve branches were recorded in the fascicles and rootlets of the lower thoracic, lumbar, and sacral nerve roots. During identifical stimulating and recording conditions, the amplitude as well as presence or absence of the evoked responses recorded was variable within the various roots. The amplitude of the evoked responses or their absence depended on the number of fibers within a particular fascicle which conducted impulses to the urinary bladder or the urethral and anal sphincters. By this method, it was determined that there was segregation or compartmentalization of the nervous innervation to the urinary bladder and sphincters within the spinal roots. In addition, the segmental spinal cord origin of the innervation of the urinary bladder was determined for the Rhesus monkey and chimpanzee. In the Rhesus monkey, the pelvic nerves to the urinary bladder arose from the first and second sacral segments and to a much lesser extent from the seventh lumbar segment. In the chimpanzee the sacral segments one to four gave rise to innervation of the urinary bladder.