Five hybrids reactive with monoclonal antibodies against human leukocyte common antigen (T-200) and/or lymphocyte function-associated antigen 1 (LFA-1) beta subunit were obtained from the fusion of human blood lymphocytes or T-cell chronic lymphocytic leukemia cells with BW5147 mouse T-cell leukemia cells. Chromosome analyses of 20 clones showed concordance between the presence of human chromosomes 1 and 21 and the expression of T-200 and LFA-1 beta subunit, respectively. Confirmation of human chromosomes in the hybrids was made by the electrophoretic analyses of phosphoglucomutase for chromosome 1 and superoxide dismutase for chromosome 21. The results suggested that the presence of human chromosomes 1 and 21 was essential for the expression of T-200 and LFA-1 beta subunit, respectively.