We developed a new monoclonal antibody (mAb), named 1E9, which recognizes the immunoglobulin (Ig) M-like molecule of the insectivore laboratory animal, the suncus. This mAb was developed in order to investigate the distribution of surface Ig (sIg)-bearing lymphocytes in the lymphoid tissues of this animal. Immunohistochemically, the distribution of 1E9+ lymphocytes in the follicles of peripheral lymphoid tissues showed homology with such distribution in rodents. However, the lymphocytes in the follicles of the mucosal lymphoid tissues were not recognized by the mAb. These data suggest that from a comparative immunological viewpoint, our newly developed 1E9 mAb is useful for the characterization of sIg+ lymphocytes in the peripheral and mucosal lymphoid tissues of the suncus.