Embryonic mouse first mandibular molars (day 18), containing the first overtly differentiated odontoblasts, were treated with EDTA or trypsin, to obtain isolated dental papillae. Trypsin dissociation was accompanied by disappearance of the basal lamina. EDTA-treatment removed the basal lamina from the basal surface of the epithelium, but left it associated with the dental papillae. EDTA- or trypsin-isolated dental papillae were grown for three to 24 h at the top of a plasma clot. Trypsin-isolated dental papillae rapidly lost their typical morphology, and the post-mitotic odontoblasts never became functional. EDTA-isolated dental papillae remained covered by the basal lamina for 15 to 18 h. During this period, the typical morphology was maintained, and post-mitotic odontoblasts secreted predentin. Preodontoblasts and odontoblasts went through the basal lamina and migrated at the outer surface of the basal lamina (i.e., at the side facing away from the enamel organ).