A uniquely low incidence and death rate of interstitial pneumonia after allogeneic bone marrow transplantation for haemopoietic malignancy is described. Deduced from the comparison with results from a multicenter study, we conclude, that a) reduction of the dose rate to less than 5 rad/min, b) exclusion of CMV pos platelet donors and c) application of a CMV hyperimmune globulin are effectful means to reduce this most often deathly complication after BMT for haemopoietic malignancy.