We describe two patients who developed respiratory syncytial virus (RSV) pneumonia after BMT. One died of RSV pneumonia after three courses of steroid pulse therapy. Surprisingly, RSV antigen was identified in the bronchoalveolar lavage fluid (BALF) obtained post mortem. Steroid pulse therapy might have suppressed anti-RSV immunity, leading to persistent RSV infection for more than 1 month. The other patient received donor lymphocyte infusions (DLI) for relapsed plasma cell leukemia, while having active RSV pneumonia. His respiratory condition improved after DLI, and RSV antigen disappeared in BALF and nasal swabs. DLI might be effective in cases of life-threatening RSV pneumonia.