The killing of endothelial cells either by activated neu-trophils or by addition of H2O2 has been extensively studied. Several different, important themes related to the mechanism of cell killing have recently emerged. 1) Depending on their origin, the susceptibility of endothehal cells to oxidant-mediated killing by neutrophils varies. 2) In some respects, the killing of endothelial cells by activated neutrophils involves a participation of en-dothelial cells in their own destruction. 3) The killing of endothelial cells by products of neutrophils does not oc-cur by a single, commonly accepted biochemical event. 4) Endothelial cell killing appears to be mediated by synergistic interaction of oxygen products and proteases from leukocytes. 5) Finally, endothelial cells can be modified by contact with cytokines such that their susceptibility to killing by neutrophils is greatly enhanced.