There were two cases of fatal interstitial pneumonia secondary to bleomycin sulfate administration. Although bleomycin pulmonary toxicity is generally thought to be dose-related and occurs infrequently with a total cummulative dose less than 300 to 400 units, the two reactions reported here occurred with doses of 105 and 165 units. Fatal bleomycin-induced pneumonia has been previously reported at these low dosages, and physicians should be aware that this toxic reaction may occur as an idiosyncratic response. Previous thoracic irradiation may be a predisposing factor. Patients receiving bleomycin should be meticulously monitored by interrogation for cough, dyspnea, and chest pain; by auscultation for rales; by serial chest roentgenograms; and by determinations of vital capacity and single-breath carbon monoxide diffusing capacity.