During dentinogenesis the expression of extracellular matrix (ECM) proteins by (pre)odontoblasts changes concomitantly with the stage of differentiation. Of these ECM proteins some are present throughout all stages of dentinogenesis, while others can only be demonstrated at particular stages of differentiation. Utilizing immunohistochemical techniques, positive detection of ECM proteins within the (pre)odontoblast or in their extracellular matrices has been demonstrated for (pro)collagen type I, III, IV, V and VI, fibronectin, tenascin, laminin, basement membrane heparan sulfate, nidogen, dentinophosphophoryns (DPP), osteocalcin (OC), osteonectin, osteopontin and 95 kDal glycoprotein. Early predentin before onset of dentin mineralization also reacts with antibodies to enamel matrix proteins. Of these ECM proteins, only DPP are exclusively synthesized by odontoblasts; DPP thus can be regarded as specific biochemical markers for odontoblast activity. A second marker for odontoblasts (but also synthesized by osteoblasts and osteocytes) is OC. In some species however OC levels in dentin seem very low. The initiation of dentin mineralization may be a matrix-mediated process in which preameloblasts also seem to be involved. Current data suggest that the DPP-collagen complex is associated with the mineralization process in dentin.