A single injection of endotoxin P45 Poly Serratia marcescens was used to induce endothelial injury in rabbits. The aortic endothelium was examined by Scanning Electron Microscopy (SEM), at various times after administration of endotoxin, using the technique of silver staining and pressure fixation. Within one hour after injection, some endothelial cells were curled-up and spindle-shaped in appearance. Areas of aorta devoid of endothelial cover were occasionally observed and platelets were sometimes found adhering to these sites. Two and four weeks after initial injury no spindle-shaped cells were found. Instead, some endothelial cells were heavily stained with silver. Small denuded zones were still found and these were surrounded by brightly silver-stained cells. This study confirms that endotoxin rapidly causes endothelial injury and suggests that regenerating endothelial cells which were formed following injury are avidly stained by silver salts and appear as bright cells by SEM.