It has been suggested that polymorphonuclear cells (PMNs) are required for the development of the adult respiratory distress syndrome (ARDS). We investigated the occurrence of ARDS with acute respiratory failure in 30 children with severe neutropenia (less than 500 PMNs/mm3) who met the clinical diagnostic criteria for ARDS and in whom postmortem histopathology findings were available within 7 days of the onset of ARDS. In 26 patients the histopathology was consistent with ARDS. In 12/26 children no white blood cells (WBC) were found in the lung tissue, 10/26 had moderate infiltration of mononuclear cells, 2/26 had massive tumor cell infiltration, and in 2/26 PMNs were found. Thus, in at least 22/26 patients ARDS developed without neutrophilic infiltration of the lungs. The maximum active lung infection rate was found to be 69% (18/26) by endotracheal and post mortem lung cultures and histology. Thus 5/26 children had ARDS without any WBC in the lung tissue. We conclude, as have other studies in adults that the absence of PMNs does not protect children from the development of ARDS and that the mechanism which involves PMNs is probably only one of several pathways for diffuse alveolar damage, some of which is neutrophil-independent.