To develop hybridomas secreting monoclonal antibodies to be used as unlimited sources of reagents indispensable for the diagnosis and treatement of leukemic malignancy, a monoclonal antibody was generated to human pre-T leukemia cells (Jurkat). Hybridomas were produced against Jurkat cell line by fusing spleen cells from hyperimmunized mice with murine plasmacytoma cells (P3$ imes$63Ag8. V653). One monoclonal antibody derived from this fusion, designated DMJ-2 was reactive with T-cell lines (Jurkat, Molt-4 and RPMI-8402) and normal peripheral E-rosette forming T cells, but unreactive with B-cell lines (Daudi, Nalm-6) and non-T, non-B cell line (K562). Conclusively DMJ-2 reactive with mature and immature T-lineage lymphoid cells.