Bronchiolitis obliterans syndrome (BOS) and idiopathic pneumonia syndrome (IPS) cause high mortality and impaired survival after allogeneic hematopoietic stem-cell transplantation (allo-HSCT). Early recognition of patients at high risk of developing BOS/IPS may lead to improving the outcome of allo-HSCT. We retrospectively analyzed serum surfactant protein A, D (SP-A, -D) and Kerbs von Lungren 6 Ag (KL-6) levels before allo-HSCT in 56 patients who survived more than 90 days after allo-HSCT and compared values of these serum markers and other transplant factors in BOS/IPS patients with those in non-BOS/IPS patients. Five patients developed BOS and two developed IPS at a median interval of 303 and 117 days (range, 100-452 and 95-153) from transplantation. As a result of univariate analysis, pretransplant serum SP-D levels but not SP-A, KL-6 in BOS/IPS patients were significantly lower than those in non-BOS/IPS patients (P=0.03). In multivariate analysis, the patients with lower pretransplant serum SP-D level had a trend toward frequent development of BOS/IPS (P=0.08). Constitutive serum SP-D level before allo-HSCT may be a useful, noninvasive predictor for the development of BOS/IPS.