The cell bodies of the lumbar sensory and sympathetic pre- and postganglionic neurons that project in the caudal lumbar sympathetic trunk of the cat have been labeled retrogradely with horseradish peroxidase applied to the central end of their cut axons. The application was made just proximal to the segmental ganglion that sends its gray rami to the L7 spinal nerve, and so identified the sympathetic outflow concerned primarily with the vasculature of the hindlimb and tail. The numbers, segmental distribution, location, and size of the labeled somata have been determined quantitatively. Labeled cell bodies were found ipsilaterally, but the segmental distributions of the different cell types were not matched. Afferent cell bodies lay in dorsal root ganglia L1-L5 (maximum L4), preganglionic cell bodies in spinal segments T10-L5 (maximum L2/3), and postganglionic cell bodies in ganglia L2-L5 (maximum L5). Both numbers and dimensions of labeled dorsal root ganglion cells were variable between experiments (maximum about 1,000); the majority were small relative to the entire population of sensory neurons. Labeled preganglionic cell bodies were located right across the intermediate region of the spinal cord, extending from the lateral part of the dorsolateral funiculus to the central canal. The highest density of labeled neurons lay at the border between the white and gray matter (corresponding to the intermediolateral cell column) with smaller proportions medially in L1-L2, and laterally in caudal L4-L5. Medial preganglionic neurons were generally larger than those lying in lateral positions. From the data, it is estimated that about 650 afferent, about 4,500 preganglionic, and some 2,500 postganglionic neurons project in each lumbar sympathetic trunk distal to the ganglion L5 in the cat.