The immunophenotyping (IPT) of lymphocytes (from lysed whole peripheral blood samples) was carried out to confirm the diagnosis of CLL using the following monoclonal antibodies (Beckman Coulter); CD45, CD5, CD19, CD20, CD22, CD23, kappa and lambda light chains, FMC7, and CD79b. The gene discussed is MS4A1; the disease is B-cell chronic lymphocytic leukemia.