Embryonic development requires extensive interaction between cells; cell-to-cell communication through gap junctions may be one mechanism involved. Much correlative evidence suggests gap junctions are involved in cellular interactions during development. Recently, the biological role of junctions has been investigated using antibodies prepared against the major rat liver gap junction protein. Disrupting normal patterns of intercellular communication with such antibodies can drastically perturb development. Recent experiments emphasize, in particular, the importance of gap junctional communication for patterning processes.