While half of all patients receiving bone marrow transplantation (BMT) for malignancies and related diseases may achieve prolonged disease-free survival, 2-10% of patients undergoing allogeneic transplantation develop bronchiolitis obliterans (BrOb). We have hypothesized that total body irradiation (TBI) which has been used for pretreatment may influence the subsequent development of BrOb in patients undergoing allogeneic BMT. Since 1976, we have treated 104 patients undergoing allogeneic BMT with non-TBI preconditioning. Of 60 patients that survived and were evaluable for chronic graft versus host disease (GVHD) 26 developed chronic GVHD (43%). Four of 104 patients (3.9%) developed BrOb by clinical and/or pathologic findings. Four of 4 patients (100%) with BrOb had chronic GVHD. Two of these 4 patients (50%) were alive at the end of 2 years. These data demonstrate that chronic GVHD is a risk factor for BrOb in patients receiving non-TBI preconditioning regimens. The similar incidence of BrOb in this population compared to other studies using TBI suggest that the preconditioning regimen is not a factor in the development of BrOb. Further study is needed to confirm these findings. Allogeneic bone marrow transplantation (BMT) has revolutionized the therapeutic approach toward acute and chronic leukemias, aplastic anemia and rare immunodeficiency disorders. Half of all patients that undergo BMT achieve long-term disease-free survival but a similar number develop significant complications [1].(ABSTRACT TRUNCATED AT 250 WORDS)