A photochemical reaction was used to produce focal microcirculation disorders in the guinea pig cochlea. Temporal bones were removed at various intervals between 5 minutes and 1 month after infusion of rose bengal (RB) and illumination. Infused but unilluminated contralateral cochleae served as controls. Dissected cochlear structures were stained by 3,3'-diaminobenzidine (DAB) peroxidase substrate medium. After observation by light microscopy (LM), the same specimens were processed and observed by scanning electron microscopy (SEM). Dilation of strial capillaries and destruction of strial epithelial cells became apparent at 1 hour after illumination. Tightly packed red blood cells were found filling the severed end of markedly dilated strial capillaries at 24 hours after the procedure. DAB staining of the osseous spiral lamina indicated vascular change with vessel dilation in the illuminated area. At 1 week after illumination, the lesion area of the stria vascularis and spiral prominence was replaced by a layer of larger, flat cells. At 1 month after illumination, all vascular supply to the cochlear lateral wall disappeared at the site of illumination. All lesions remained focal and showed no sign of expansion or reduction throughout the observation period. The cochlear duct of the guinea pig appears to be segmentally nourished by the capillary system. Observation of DAB stained tissue by LM and SEM proved to be informative in the study of microcirculation disorders of the inner ear.