FIELD : medicine.SUBSTANCE : present invention relates to medicine, in particular to a method for treating a B-cell malignant disease, which is selected from the group consisting of non-Hodgkin' s lymphoma, acute lymphoblastic leukaemia and chronic lymphocytic leukaemia.EFFECT : implementation of the invention allows to increase the uptake of anti-CD20 antibodies by a tumour by increasing the level of CD20 by pre-administration of 177Lu monoclonal antibody HH1.9 cl, 7 ex, 6 dwg