Intercellular communication of notochord cells during their differentiation was studied by microinjection of a fluorescent dye, Lucifer Yellow. Close correlation existed between the incidences of dye coupling and quantitative evaluation of gap junctions. High incidences of dye coupling and of gap junctions occurred at a stage when notochord cells were active in the change of cell shape and cell arrangement. With the subsidence of cell movements,both dye coupling and gap junctions were reduced to lower levels. It was, therefore, suggested that intercellular communication via gap junctions played an important role in the coordination of notochord cell movements. Gap junctions of altered configuration occurred in notochord cells in late tailbud stage. The comparison of incidences of dye coupling at this stage with those at other stages strongly suggested that the gap junctions of altered configuration functioned just as those of generalized type. Intercellular communication of notochord cells during their differentiation was studied by microinjection of a fluorescent dye, Lucifer Yellow. Close correlation existed between the incidences of dye coupling and quantitative evaluation of gap junctions. High incidences of dye coupling and of gap junctions occurred at a stage when notchord cells were active in the change of cell shape and cell arrangement. with the subsidence of cell movements, both dye coupling and gap junctions were reduced to lower levels. It was, therefore, suggested that intercellular communication via gap junctions played an important role in the coordination of notochord cell movements. Gap junctions of altered configuration occurred in notochord cells in late tailbud stage. The comparison of incidences of dye coupling at this stage with those at other stages strongly suggesting that the gap junctions of altered configuration functioned just as those of generalized type.