Objective     To investigate the expression of the helix-loop-helix (HLH) transcription factor Id2 (inhibitor of DNA binding-2) in spinal cord of adult rats.      Methods     Immunohistochemistry was performed on the sections of spinal cord of rats perfused with Zambonis.      Results     The positive Id2-immunoreactive cells distributed in the spinal cord extensively. In lamina Ⅰ-Ⅲ

the expression of Id2 was predominantly in nucleus and few in cytoplasm

the same as lamina Ⅸ. In lamina Ⅳ-Ⅷ

positive Id2 immunoreactivity was present in both cytoplasm and nucleus. The volume of positive cells was larger and their staining got deeper from lamina Ⅳ to lamina Ⅷ gradually.       Conclusion     Id2 protein is widely distributed in grey matter of spinal cord of rats. The cellular location of Id2 different in laminas might be associated with cell type.