Insulin-like immunoreactive neurons were localized in the cervical, thoracic, lumbar and sacral segments of the monkey spinal cord. Both dorsal and ventral horn cells were labelled. Insulin-like reaction product was localized in the cell nucleus and cytoplasm. Both inner and outer nuclear membranes were labelled. Reaction product appeared to be scattered throughout the nucleoplasm but not within the nucleolus. In the cytoplasm, labelling was mainly localized in the cisternae of rER and saccules of Golgi apparatus. Both proximal and distal dendrites were labelled, the reaction product was closely associated with the parallel arrays of neurotubules. Most of the distal dendrites were postsynaptic to non-labelled axon terminals; however, some were postsynaptic to lightly labelled axon terminals. A labelled dendrite often formed the central element of a synaptic glomerulus with several nonlabelled axon terminals. It is hypothesized that insulin-like substance(s) may be modulating nuclear activities as well as neuro-transmission at the synapse.