Bone marrow stromal cell changes in haematological malignancies. Stromal cell numbers from subjects with no haematological disease and those with acute myeloid leukaemia (AML), chronic granulocytic leukaemia (CGL), acute lymphatic leukaemia (ALL) and non-Hodgkin's lymphoma (NHL) were compared to determine their role in malignancy. Frozen sections of trephine biopsy specimens from iliac crests were stained for endogenous alkaline phosphatase activity, endogenous acid phosphatase activity, and, using immunocytochemical methods, for endothelial cells (anti-factor-VIII related antigen) and macrophages and related cells (EBM/11). In granulocytic malignancies, whether acute or chronic, alkaline phosphatase positive reticulum cells (AL-RC) and vascular endothelial cells were generally increased. In lymphoid malignancies, the numbers of AL-RC were generally reduced. Numbers of vascular endothelial cells seemed to be normal in ALL but reduced in foci of NHL. Macrophages are numerous in normal marrow, and their numbers seemed to be normal in granulocytic lesions but were more variable and sometimes reduced in ALL and NHL. Lymphoid malignancies, therefore, have a destructive effect on some stromal elements; granulocytic malignancies are associated with normal or increased numbers of stromal cells. A possible consequence of depleted stromal cells might be slower reconstitution of normal haemopoiesis after treatment. The large numbers in granulocytic malignancies raises the possibility of synergistic stimulation between stromal and neoplastic cells. 