The neutrophil is a key element in host resistance to bacterial infection. Bacterial products capable of subverting the antimicrobial properties of neutrophils can have a potentially deleterious effect on the host. Current knowledge of the effects of endotoxins derived from the outer cell envelope of gram-negative bacteria on neutrophil function is summarized. Available evidence indicates that endotoxins bind to neutrophils, both in vitro and in vivo. The lipid A region of the endotoxin macromolecule appears to be important in promoting the association of endotoxin with the neutrophil cell membrane. Endotoxin-neutrophil interactions can result in altered neutrophil adhesive and locomotory properties. Moreover, endotoxins have been demonstrated to induce selective degranulation of specific (secondary) granule constituents and to alter the oxidative and microbicidal properties of the neutrophil. Further studies are needed to define on a molecular level the nature of the endotoxin receptor, the precise structural components of endotoxin responsible for altering neutrophil behavior, and the transductional event(s) leading to neutrophil activation as a result of endotoxin exposure.