Glycoconjugates with terminal galactose residues were localized in rat spinal cord and spinal ganglia using lectin-HRP conjugates of Griffonia simplicifolia and Glycine max agglutinins. Alternate staining of serial sections with HRP-labelled lectins and an antibody for substance P (SP) showed staining in identical primary sensory neurons with both methods. Similarly, lectin-reactive as well as SP-positive fibers were found in Rexed laminae I and II, Lissauer's tract, the spinal nucleus and tract of the trigeminal nerve, the nucleus commissuralis and a small bundle of fibers just ventral to the central canal. Administration of capsaicin to neonatal rats produced a significant decrease in lectin-reactive fibers of the substantia gelatinosa, and in the number of lectin-reactive sensory neurons. The coexistence of SP with galactose-containing glycoconjugates in spinal ganglion neurons, as well as sensitivity of these cells to capsaicin, provided a basis for classifying the reactive neurons as nociceptive in type. Ligation of dorsal roots resulted in disappearance of lectin reactivity in the spinal cord and caused accumulation of lectin-positive material proximal to the ligature, indicating somatofugal transport of galactose-containing glycoconjugates. Colchicine injection caused an increase in SP reactivity in dorsal ganglion neurons but no change in lectin staining of galactoconjugate. At the ultrastructural level affinity for the lectin conjugates was confined to the Golgi cisternae and the plasmalemma of B-type sensory neurons in the dorsal ganglion. The axolemma of unmyelinated processes stained selectively in dorsal roots and the substantia gelatinosa of the spinal cord. These findings provide evidence for the presence in certain sensory cells of a characteristic galactosylconjugate which may prove to be of significance in nerve function.