The occurrence of pulmonary disease associated with long-term BCNU therapy is reported in two patients treated for astrocytoma grade II whose clinical presentations of pulmonary complications and corresponding tissue alterations showed striking differences. One patient presented with a dramatic, fulminating, and rapidly fatal pulmonary disease. His lungs revealed atypical proliferation of pneumocytes, moderate interstitial inflammation, fibrosis and intra-alveolar hyalin membranes. The second patient presented with slowly progressive dyspnea, ultimately leading to death secondary to severe diffuse alveolar septal fibrosis. Individual differences in response to toxicity are suggested and discussed.