Autoradiographic studies revealed concentration of 3H 1,25(OH)2 vitamin D3 in nuclei of certain neurons in the spinal cord of adult and neonatal mice, fed a normal or a vitamin D deficient diet. Nuclear uptake and retention was strongest in motor neurons in lamina IX. Nuclear concentration also existed in neurons of lamina II, lamina VIII, lamina X and intermediate nucleus of the lateral column. The results indicate that these neurons are target neurons which contain nuclear receptors for 1,25(OH)2 vitamin D3. This suggests that 1,25(OH)2 vitamin D3 has direct genomic actions on the innervation of skeletal muscle by exerting related trophic, secretory, and electrophysiological effects. In addition, these data point to direct genomic actions of 1,25(OH)2 vitamin D3 on spinal sensory perception, and on certain autonomic functions. Nuclear binding in certain neurons in the peripheral ganglion of the trigeminal nerve further suggests that sensory perception is influenced by 1,25(OH)2 vitamin D3 not only at the level of the substantia gelatinosa, but also at the level of spinal ganglia.