PURPOSE: To enable the detection of an ATLA antibody specifically, by the reaction of specimen serum and a labeled human immunoglobrin G antibody with an adult T-cell leukemia (TAL) cell cultivated as antigen.

CONSTITUTION: An ATL cell cultivated after sampled from an ATL patient by blood collection or the like is used as antigen. One drop of a specified concentration liquid of the cultivated cell is applied, dried and fixed on a slide glass and specimen serum is added in one drop which is diluted on a half-by-half basis to cause an immune reaction. Then, human immunoglobulin G antibody labelled with a fluorescent substance or enzyme is caused to react upon the reactant. ATLA (ATL antigen) formed in fixed cultivated ATL cell is combined with an ATLA antibody in the specimen serum to form a complex conjugate with the labelled globulin G antibody. The presence of fluorescence due to the above conjugate of the labelled substance localized in the cell is determined with a microscope whereby the ATLA antibody can be determined at a high accuracy by the maximum dilution ratio of the fluorescent positiveness. Thus, discrimination can be made from other leukemia and malign diseases.