Infusion of LPS into sheep has been shown by Brigham and colleagues (6) to produce neutropenia and neutrophil sequestration in the lung, followed by increased lung vascular permeability. The latter effect was abrogated by neutrophil depletion. Similar, though variable, data havebeen obtained in lung injury in monkeys (7) and dogs (8). The effects of LPS injection have frequently been ascribed to complement activation, since LPS may activate complement by both alternate and classicalpathways (9). However, studies by a number of groups have suggested that complement activation per se is unable to simulate the effects of LPS (10-12).

However, Dahinden and colleagues (13) have argued that LPS may directly enhance neutrophil adherence to plastic in vitro, whereas Yamada and colleagues (14) as wellas our own unpublished observations (Tonnesen, etal.) indicate that LPS enhances neutrophil adherence to endothelial cells. Weshow in a companion report (15) that LPS may directly promote rabbit neutrophil sequestration in the pulmonary vasculature in vivo. Although the adherence of neutrophils to endothelium is likely to be the first step in neutrophil-mediated injury, the sequestration of neutrophils within the pulmonary vasculature by itself appears in-