The distribution of the vitamin D-dependent calcium-binding protein, calbindin, was mapped in the brachial spinal cord and in the 15th dorsal root ganglion of the domestic fowl, using fluorescence immunohistochemistry. Cell somata of the dorsal root ganglion ranged in area from 200 microns 2 to 2000 microns 2. Sixteen percent of cell bodies displayed calbindin immunoreactivity. Reactivity occurred in both the small and large sensory neurons. These were randomly distributed within each ganglion. In the spinal cord, calbindin immunoreactivity was intense in Lissauer's tract, and in nerve fibres and nerve cell bodies within laminae 1 to 3 of the dorsal horn. Scattered varicose fibres were observed in laminae 4 to 7. Immunoreactivity was intense in laminae 10 where nerve fibers formed a meshwork around the central canal. Immunoreactive perikarya were occasionally observed in the outer region of lamina 10 and between laminae 8 and 9. The perikarya of the large motoneurons of lamina 9 were not reactive although they were enmeshed in calbindin-immunoreactive fibres.