AIM: To investigate whether spinal cord transection induces changes of gene expression of S 100A4 protein.METHODS: In a spinal cord transection model, S 100A4 expression and cellular localization were examined using cDNA microarray, Northe blot, immunohistochemistry, and immunofluorescence double-labeling methods.RESULTS: There was very limited S 100A4 mRNA expression in the control spinal cord. However, S 100A4 mRNA expression was increased significantly in both the rostral and caudal spinal cord segments adjacent to the injury site.Specifically, S100A4 gene expression was substantially increased at d 2, peaked at d 7 and d 14, and remained high up to 28 d post-injury. During its peak expression, S100A4 protein was localized in astrocytes of the spinal cord within 5 mm from the site of spinal transection. CONCLUSION: Spinal cord transection induces prolonged S 100A4 expression at both mRNA and protein levels in areas close to the injury site. Increased expression of S100A4 in astrocytes after spinal cord transection may indicate that this molecule may play a role in astrocytic responses to injury.