To investigate whether the MCs of colon mucosa is elevated in IBS, and to eluciate their possible roles in IBS, biopsies of the terminal ileum, ICJ, ascending colon, and sigmoid colon were stained specifically with histochemistry for the MCs in 15 controls and 28 patients with IBS. The results were investigated qualitatively and quantitatively by color image analyzer. The structure relation between MC and nerves or cells was studied by ultramicroscopy. The results showed the number of MCs in the terminal ileum, ICJ, and ascending colon, was significantly elevated in IBS( P