The labyrinths of guinea-pigs sensitized by horseradish peroxidase (HRP) were investigated by electronmicroscopy after challenging this antigen through the foram. stylomastoideum. Horizontsl nystagmus toward the contralateral side was observed about fifteen minutes after challenging. The animals sacrified in this stage did not show endolymphatic hydrops, however, particles of HRP were observed in intracellular vesicles and basal lamina of Reissner's membrane. This particles were took in dark cells of the stria vascularis, too. In the animals sacrified three days after challenging HRP, endolymphatic hydrops could be observed. These findings were not observed in the control study and suggested that hyperpermeability of the Reissner's membrane and hypersecretion of the stria vascularis induced by antigen-antibodyreactions were probable causes of endolymphatic hydrops.
