The distribution of the cell adhesion molecule C-CAM was analyzed during tooth development, eruption and formation of the junctional epithelium in rat molars by immunohistochemistry and in situ hybridization. C-CAM could not be detected during odontogenesis until the late bell stage; then only the mRNA was demonstrated in the odontoblasts and ameloblasts. Prior to eruption, a local increase in C-CAM (mRNA and protein) was observed in the reduced enamel epithelium. During eruption, high C-CAM levels were seen in the fusion zone between the oral epithelium and the reduced enamel epithelium. In the adult rat, C-CAM remained strongly expressed in the junctional epithelium. Our study indicates that C-CAM may play a role in odontogenesis and during formation of the epithelial structures involved in tooth eruption and formation of the junctional epithelium.