Using intracellular injection of small fluorescent molecules, we examined the gap-junctional communication properties of cells in the wing imaginal disk of Drosophila. We observed extensive spread of the injected dye between cells in all parts of the wing disk epithelium, but we found that this spread is not uniform. Instead, the cell-to-cell movement of dye is partially restricted at several defined boundaries such that cells on one side of the boundary have a low level of communication with cells on the other side. These communication-restriction boundaries are delineated by bands of cells with a low level of communication, and they subdivide the disk epithelium into a number of "communication compartments." Interestingly, the boundaries of some of these communication compartments appear to be coincident with compartment borders identified in cell lineage studies. Given this striking coincidence, we suggest that gap-junctional communication may play a role in compartment formation, and in controlling the appropriate differentiation of cells within compartments.