CD5 is expressed in some B- cell derived lymphoproliferative disorders, notably chronic lymphocytic leukaemia (CLL) (> 90%) (1, 2), and centrocytic leukaemia. CD19 monoclonal antibody also reacts with pre-B-cell- lines, B lymphoblastoid cell-lines and Burkitt cell- lines, and with 50% of myeloma cell-lines. Virtually all non T-ALL, B-CLL and B-cell lymphomas were found to be positive, myeloma cells were found to be negative. This product can be used for evaluation of residual disease in B-cell chronic lymphocytic leukemia patients and bone-marrow remission.