B-cell chronic lymphocytic leukaemia (CLL) is characterised by a monoclonal expansion of small B lymphocytes, typically expressing CD5, CD19, CD23 and low levels of surface immunoglobulin (Ig) (Matutes et al, 1994), which previously were supposed to originate from naive B cells of the mantle zone. The gene discussed is FCER2; the disease is B-cell chronic lymphocytic leukemia.