Prolonged pre-transplant IFN administration in patients with chronic myeloid leukaemia has been associated with an increased risk of fatal transplant-related complications and an inferior outcome after allogeneic bone marrow transplantation. Using a two-stage long-term bone marrow culture as an in vitro model we were able to show a negative effect of higher doses of IFN pre-treatment of bone marrow stroma on haematopoesis. This correlated with a decline in the number of monocytes-macrophages. While monocytes-macrophages itself produce cytokines, a vicious circle may lead to an ineffective function of the microenvironment resulting in ineffective haematopoieses and increased transplant-related complications.