The study was carried out to investigate ultrastructural changes and circulatory disturbances of inner ear, particularly in stria vascularis, in endotoxemia with could occur in various bacterial infections. Guinea pigs were given bacterial endotoxin(E. coli 026 : B6, Bactolipopolysaccharide), and the stria vascularis was morphologically observed. The control group received double injections of 0.5 ml of saline intravenously with 24 hours interval and observed at 24 hours after the last injection. The experimental group was given double injections of 4 mg endotoxin in 0.5 ml saline intravenously with 24 hours interval and observed at 24 hours after the last injection. Five guinea pigs were used in each group. The stria vascularis was studied by means of light microscopy, electron microscopy, and enzyme cytochemical electron microscopy by using the horseradish peroxidase(HRP) as a tracer to observe vascular permeability. On light microscopy, the stria vascularis was slightly edematous. On electron microscopic study, widening of intercellular spaces between the marginal cells, swelling of the intermediate cells with vacuolar change and increase of lysosomes, marked increase of capillary permeability without leakage of HRP into the endolymphatic space and spiral ligament, and presence of pinocytosis of HRP positive product in the intermediate cells. From the above results, it would be considered that bacterial endotoxin caused incerase of capillary permeability in the stria vascularis and degradation of intermediate cells. These changes may also induce alteration of constituents of endolymph. Furthermore, functional disturbances of inner ear may occur.