The cell bodies of thoracolumbar sensory and sympathetic pre- and postganglionic neurons that project to the colon and pelvic organs of the male rat were labeled retrogradely with horseradish peroxidase (HRP) in order to study numbers, segmental distribution, and location of the somata of these neurons quantitatively. HRP was applied to one hypogastric nerve (HGN), to the lumbar colonic nerves (LCN) and to the intermesenteric nerve (IMN). In order to estimate the significance of the branching of one axon into both hypogastric nerves a double-labeling technique with fluorogold and HRP was used. About 2640 neurons project into the two HGN added together (800 afferent, 1320 pre-, and 520 postganglionic), 4650 neurons into the LCN (360 afferent, 0 pre- and 4290 postganglionic), and 5990 into the IMN (1500 afferent, 1250 pre-, and 3240 postganglionic). About 4190 sympathetic postganglionic prevertebral neurons innervate the colon and pelvic organs, 1900 are located in the inferior mesenteric ganglion and 2290 in ganglia of the IMN. Considering the efferent component, the HGN mainly are preganglionic and the LCN exclusively postganglionic nerves. Branching of one axon into both HGN is a rare event and quantitatively negligible (less than 3%). Afferent neurons of all three nerves were found in the dorsal root ganglia (DRG) T12-L2 with the maximum in L1 and L2. The distribution of afferent neurons projecting into the LCN is shifted slightly more rostrally compared to neurons projecting into the HGN. The IMN distribution is located in a position in between. Preganglionic neurons projecting into the IMN are located in the spinal cord segments T12-L3 with the maximum in L1 and L2.(ABSTRACT TRUNCATED AT 250 WORDS)