Six monoclonal antibodies (MAbs) (4 IgG3 and 2 IgM) were produced by hybridomas obtained from A/J mice immunized with EL4(C57BL/6 derived-T lymphoma). They were found to react with antigens expressed on both mouse and human T-lymphomas but not on B lymphomas or normal cells. All of these antibodies reacted with the disialoganglioside GD2, GalNAc beta I----4(NeuAc alpha 2----8NeuAc alpha 2----3)Gal beta I----4Glc-Cer, by 3 different assay systems including the immune adherence inhibition test, enzyme-linked immunosorbent assay, and enzyme immunostaining on thin-layer chromatography. The binding specificities of these MAbs to disialogangliosides differed. Four MAbs (AI-201, AI-287, AI-410, and AI-425) showed restricted specificities, detecting only GD2, whereas the other 2 (AI-245 and AI-267) had a broader specificity, recognizing GD2, GD3, and GDlb. No evidence was obtained for the presence of the antigenic epitope in glycoproteins of mouse and human tumor cells. The ganglioside content of EL4 was low in comparison with that of M14 (a human melanoma cell line).