The thoracic sympathetic preganglionic outflow is important in the maintenance of postural normotension in man. Normative data on the intermediolateral column (ILC) neuron cell bodies is lacking. Counts and measurements on the right ILC cytons have been performed on the T6, T7 and T8 segments of 12 spinal cords of man obtained within 4-6 h of death. A methodology was employed which has been optimized to prevent shrinkage of cytoplasm from the neuropil and which mathematically corrects the number of cytons of neurons and their frequency distribution for split cell error. The mean cyton counts for T6, T7 and T8 spinal cord segments were 5002, 5004 and 4654 respectively. No significant sex difference was shown. Most cytons ranged in diameter from 8-23 micrometer; the major peak in the size histogram is at 12-13 micrometer and a smaller peak is seen at 16 micrometer. There is a progressive reduction of ILC cytons with age. In adult man approximately 370 cytons (approximately 8%) are lost per decade. This reduction in ILC cytons with age may be a morphological basis for postural hypotension of the aged.