Quantitative estimations of the density of localisation of propriospinal interneurons with descending transsegmental axons were obtained for the spinal cord of cat. Neurons were labelled by unilateral HRP injections at different segmental levels. Mean quantity of labelled neurons per 50 micron slice was regarded as a measure of density. The density of propriospinal neurons with the longest axons connecting cervical segments with lumbosacral ones was approximately two orders less than the density of neurons with short (up to two segments) axons and several times less than the density of neurons with axons of intermediate length. No local maxima of density of long-axon propriospinal neurons at the brachial enlargement were found. The quantity of neurons with crossed axons in most of segments reached about a half of the total number of propriospinal units. Zones of maximal concentration of propriospinal neurons with uncrossed and crossed axons of different length were defined on the cross-sections of the spinal grey at different segmental levels. Correlation of the quantitative composition of propriospinal neuronal populations with the patterns of effects transmitted by these populations are discussed.