The invention relates to pharmaceutical means and methods for the prevention, treatment or amelioration of indolent or aggressive B cell non-Hodgkin lymphoma (B NHL) and B cell leukemia comprising the administration of a bispecific single chain antibody construct to a subject and the use of the bispecific single chain antibody construct for the preparation of a pharmaceutical composition for the prevention, treatment or amelioration of indolent or aggressive B cell non-Hodgkin lymphoma (B NHL) and B cell leukemia. The construct is to be administered for at least 1 week in specified daily doses. Moreover, the invention relates to kits comprising a bispecific single chain antibody construct to be used in accordance with this invention.