Understanding the genetic control of tooth eruption is one of the major issues in tooth development. Thus far, it is known that eruption-related molecules are secreted from follicular cells surrounding the germs and are related mainly to osteoclast formation. This study examined the involvement of CD147 and its downstream molecules in the eruption of rat developing molars using immunohistochemistry, RT-PCR and histomorphometry. CD147 was expressed differentially in the cap (3rd molar germs) and root formation (2nd molar germs) stages in tooth development. CD147 was localized immunohistochemically in the follicular cells and osteoclasts as well as in the ameloblasts and odontoblasts. The expression pattern of CD147 and mmps was investigated because CD147 is an mmp inducer. The expression of both mmp-2 and -9 increased at the root formation stage compared to that at the cap stage and increased in a stage dependent manner. However, the level of mmp-13 was not changed notably. The