An immunoproliferative disorder with M component lgD/λand a strong decrease of the other Ig classes in the serum is reported. The peculiarity of this disorder consists in the shift from a predominant chronic lymphocytic leukaemic pattern, at the beginning, to a true myeloma with plasmacytic leukaemia IgD/λ several months later. The possibility of the removal, in this case, of the initial precocious block with derepression or ‘switch on’ in transformation of the malignant lymphocyte clone and, consequently, change of a type of malignant lymphoma into another more evoluted and more malignant type is disc