By the freeze-etching technique, electron microscopic observations of the formation of the tight junction of embryonic cells of Cynops orientalis were carried out. Three states were recorded: isolated fragments of junctional strands occurred at the lateral membrane, the isolated fragments connected to form a more or less continuous band and finally a typical bandlike structure was observed at the apical border of the cell. They represent the transitional stages of the polarization of the tight junction. The dependence of the polarization on the appearance of the segmentation cavity and the interrelationship between the polarization and the domains of the epithelial cells were discussed. By the freeze-etching technique, electron microscopic observations of the formation of the tight junction of embryonic cells of Cynops orientalis were carried out. Three states were recorded: isolated fragments of junctional strands occurred at the lateral membrane, the isolated fragments connected to form a They represent the transitional stages of the polarization of the tight junction. The dependence of the polarization on the appearance of the segmentation cavity and the interrelationship between the polarization and the domains of the epithelial cells were discussed.