First and second branchial arches were dissected from mouse embryos of 9-13 days gestational age. The epithelial and mesenchymal components were separated after enzymic digestion. Scanning electron microscopy did not reveal a dental lamina along the dental arches before day 12, after which the lamina was formed locally in the incisor and molar regions. There was no epithelial down-growth in the diastema region. Heterotypic recombinations of mandibular arch and second branchial arch tissues showed that early mandibular arch epithelia, before day 12, have odontogenic potential and can elicit the formation of a dental papilla in non-odontogenic, neural-crest-derived mesenchymal cells of the second arch. However, the mandibular mesenchyme must interact with mandibular epithelium in order to have the competence to induce teeth in non-odontogenic epithelium.