A mouse monoclonal antibody (G9, Horio et al. in Cell Motil Cytoskel 44:284-295, 1999) that was raised against the gamma-tubulin from a fission yeast, Schizosaccharomyces pombe, showed a unique staining in the mouse small intestine. Similar to another anti-gamma-tubulin antibody that is commercially available, G9 showed typical dot-like staining corresponding to the microtubule-organizing center in the free cells of the epithelium and the connective tissue under it. In addition, G9 stained the cell-cell contacts in the epithelium. This stained region was not bicellular but tricellular junctions of the enterocytes. This staining was unique to G9 and was diminished on the sample of the mouse small intestine, which had lost most of its filamentous microtubules through the preparation process. The tricellular junction is thought to be the weakest point of the epithelial barrier, and no other junctional structures have been identified except for the central sealing elements extending from the tight junctions between the two cells. Our results suggest the existence of a new molecule underlying the tricellular junctions, which may relate to gamma-tubulin and the microtubules.