Basement membranes of the developing tooth have been previously shown to contain laminins, but the nature of the laminins have not been described. We here studied the distribution of five different laminin alpha chains during tooth development. We show that both epithelial and mesenchymal cells produce laminin alpha chains. The mRNAs of three laminin alpha chains, alpha1, alpha2, and alpha4, were expressed in the tooth mesenchyme, whereas two, the alpha3 and alpha5 chain mRNAs, were found in epithelium. Drastic changes in the expression patterns of the two epithelial chains were found during development. The alpha5 mRNA was widely expressed in tooth epithelia, and the corresponding protein was evenly distributed along the tooth basement membrane throughout embryonic development. This suggests a role for alpha5 as a major laminin alpha chain in tooth basement membrane during embryonic stages. The subsequent disappearance of alpha5 and the drastic increase in alpha3A mRNA expression during terminal ameloblast differentiation and enamel secretion suggest that alpha3A acts as an important chain in the enamel matrix after degradation of tooth basement membrane. These studies show that laminin networks in tooth epithelia form as a result of epithelial-mesenchymal interactions and that the molecular composition of the laminin networks varies drastically during development of tooth.