Although a number of studies have suggested that granulocyte sequestration is an important pathophysiologic event in ARDS, histologic evidence of aggregated granulocytes in the pulmonary microvasculature is limited, and serial histologic data have not been reported with physiologic measurements. We report a patient with ARDS who demonstrated microvascular granulocyte aggregation and lung edema in sections of a lung biopsy obtained seven days after the onset of symptoms. Pulmonary vascular resistance and pulmonary capillary wedge pressure were normal immediately before the biopsy. A second biopsy performed 12 days later showed decreased lung edema and no evidence of intravascular leukostasis. This case provides histologic support for the hypothesis that granulocyte aggregates contribute to pulmonary edema associated with ARDS.