Soluble protein fractions obtained from bovine lumbar spinal motoneuron cell bodies, ventral gray matter, and ventral and dorsal roots were analyzed by two-dimensional gel electrophoresis. Each extract was separated into Coomassie blue-stained patterns of up to 350 polypeptides ranging in isoelectric point from pH 4 to 8 and in molecular weight from 10,000 to 200,000. Visual inspection of the protein pattern of the isolated cell bodies showed it to be substantially different from those of ventral gray matter and the spinal roots, while the patterns obtained from ventral and dorsal roots were indistinguishable. Computer-assisted densitometry of the major soluble proteins from spinal roots showed no quantitative difference between the predominant proteins in ventral and dorsal root extracts. Differences of 10-fold or more were common when the major proteins of the isolated perikarya were compared with those of the other fractions. Since most of the soluble proteins extracted from ventral and dorsal roots were probably derived from the axoplasm of motor and sensory nerves, respectively, these results are interpreted to mean that large differences exist in the distribution of individual soluble proteins between the cell body and axon of spinal motoneurons, while the major soluble proteins of spinal motor and sensory axons are highly similar.