A panel of 14 anti-shared idiotype (Sid) monoclonal antibodies selected according to their high cross-reactivity to various lymphomas was immunohistologically tested for reactivity with seven reactive lymphoid tissue specimens and 227 B cell lymphoma specimens obtained from Japanese patients. In the reactive lymphoid tissues, the anti-Sld antibodies each reacted with a subpopulation of cells in the mantle zone and interfollicular areas; they rarely reacted with cells in the germinal center. In the B cell lymphomas, 13 anti-Sld antibodies reacted with a total of 78 of 186 (42%) specimens bearing immunoglobulin; none of the antibodies reacted with 41 specimens not bearing immunoglobulin. In mantle cell lymphomas (15/19, 79%) and extranodal small lymphocytic/non-mantle cell diffuse small cleaved lymphomas (11/15, 73%), the reactivity of the antibodies was high compared with that in the other lymphomas (52/152, 34%; P = 0.0002 and 0.004, respectively), including follicular lymphomas (11/42, 27%; P = 0.002 and 0.002, respectively). Since idiotypes are associated with the hypervariable regions and antigen-binding sites of immunoglobulin, these findings may reflect the differences in the regions/sites in each of these diseases.