A typical inflammatory response resulted from the intravenous injection of endotoxin (E. coli) into living rabbits. Each rabbit was studied at three levels: the microvasculature and supporting tissue in the ear chamber was observed microscopically (up to X200) before, during, and at regular intervals following the injection of endotoxin; leucocyte and platelet counts were made periodically throughout each experiment; and tissue samples for histological study were obtained from each rabbit prior to death. The animal was anaesthetised before histological samples were secured. Within minutes after the intravenous injection of endotoxin, leucocytes were observed sticking to the endothelial cells lining the venules and the arterioles. Emboli appeared in the microcirculation within 10 min. Swelling of the microvascular endothelial cells was evident at 1 hr; oedema and extravasation of the cellular elements followed. The rectal temperature and leucocyte and platelet counts all fell within 10 min. of endotoxin. Histological examination of tissue from the ear chamber and visceral organs showed inflammatory changes. Congestion of the microvasculature, swelling of the endothelial cells, and margination and migration of neutrophils were common histological features in all organs. The earliest cells affected appeared to be the leukocyte and platelet.