The possibility that communication through gap junctions may be important during embryonic development has often been raised since gap junctions were first described between early embryonic cells. It is now known that this direct cell-to-cell communication pathway disappears between groups of embryonic cells with different developmental fates as the embryo progresses through development, suggesting that transfer through the gap junctional pathway may play some part in controlling events during development. Supportive evidence for a role for gap junctions comes from experiments demonstrating that the properties of gap junctions differ at the border separating each segment in insect epidermis. Recently it has been shown that the ability to exchange small dyes between cells in the amphibian embryo depends on the position of each cell with respect to the grey crescent. When communication through gap junctions is prevented, by injecting antibodies to gap junctions protein, pattern formation is severely disturbed in the non-communicating region. The paper describes experiments on the pattern of junctional communication at early stages of development of the amphibian embryo and illustrates how anti-gap junction antibodies are being used to determine when and where communication through gap junctions may play an important role during development.