A retrospective study of 211 bone marrow aspirates from patients with chronic myeloid leukaemia (CML) was undertaken to assess the incidence of Gaucher cells and sea-blue histiocytes. A significant correlation between the presence of these cells and prolonged survival was seen. Such storage histiocytes occurred most often during periods of relapsed chronic phase. This study shows that Gaucher cells and sea blue histiocytes are a common feature of CML and that their accumulation seems to be associated with a prolonged increase in leucocyte turnover.