The release of mast cell granules is commonly associated with inflammation and fibrosis. However, does direct communication between mast cells and fibroblasts through gap junction intercellular communication (GJIC) occur? Fibroblast populated collagen lattice (FPCL) cast with mast cells show enhanced lattice contraction. Do released granules or GJIC between mast cells and fibroblasts promote enhanced lattice contraction? Mast cells preloaded with a fluorescent dye that readily passes through gap junctions were cast in FPCL. Dye passed from mast cells into fibroblasts within these cocultured mast cell-FPCLs. Fatty acid amide hydrolase inhibitor blocks the breakdown of oleamide, which is a potent endogenous inhibitor of GJIC. GJIC was blocked for 3 days when mast cells were pulsed for 3 hours with fatty acid amide hydrolase inhibitor. Mast cells pretreated with fatty acid amide hydrolase inhibitor cast in cocultured mast cell-FPCLs failed to enhance cocultured lattice contraction. Mast cell-FPCLs made with mouse fibroblasts unable to generate GJIC failed to show enhanced lattice contraction. Degranulated mast cells were equal to intact mast cells at enhancing cocultured mast cell-FPCL contraction. The supernatant from degranulated mast cells had no effect upon FPCL contraction. Therefore, enhanced mast cell-FPCL contraction appears to be independent of mast cell granules, but dependent upon GJIC between fibroblasts and mast cells. We speculate that mast cell-fibroblast GJIC may play a role in fibrosis.