Two kinds of experimental endolymphatic hydrops were produced:one was induced by obstruction of the endolymphatic sac , and the other was induced by systemic KLH immunization and secondary KLH challenge into the endolympha tic sac. Vascular permeability of the stria vascularis was compared in the two models by light and electron microscopy using the tracer horseradish peroxi dase (HRP) method. The ratios of capillaries showing HRP leakage to capillaries observed were 7/33 in the endolymphatic

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... c obliteration model , 36/39 in the se condary challenged side, and 13/37 in the non-secondary challenged side of the immunologically induced model. Permeability to HRP was significantly higher in the secondary challenged side than in either the endolymphatic sac obliteration model or the non-secondary challenged side. The present study raises the pos sibility that endolymphatic hydrops is induced by overproduction of endolymph .