Acute respiratory failure developed in two patients with hyperleukocytic acute myelomonocytic leukemia with abnormal marrow eosinophils within 1 to 3 days after the beginning of high-dose induction chemotherapy. The presence of moderate pulmonary leukostasis before chemotherapy initiation, the simultaneous occurrence of an acute tumor lysis syndrome, the lack of evidence of any other cause of respiratory distress, and the clinical evolution lead the authors to attribute pulmonary injury to lysis of resident leukemic cells. The responsibility of eosinophilic cellular constituents for the diffuse alveolar damage is discussed.