Epithelial-mesenchyme interactions during mouse molar tooth morphogenesis were observed by electron microscopy. The basal lamina was intact from day 10 to day 18. Aperiodic, later also periodic fibrils were deposited on the basal lamina. Ectomesenchymal cell processes were always in close relation with the basal lamina or with the fibrillar material. On day 19 some direct heterotypic cell contacts between odontoblasts and preameloblasts were observed. At all stages, especially the preodontoblasts but also preameloblasts, gave rise to aggregated vesicles, which were extruded in the epithelial-mesenchymal space.