The microscopical and ultramicroscopical changes in the stria vascularis due to cis-diamminedichloroplatinum II (DDP) were studied. Sixteen healthy adult guinea pigs were used for the experiment. A standard dosage DDP (1.5 mg/kg/d) was administered over a period of 5-20 days. A clear degeneration pattern was found (ranging from no changes to cystic degeneration with protrusion of marginal cells followed by loss of marginal cells). DDP seems to be especially toxic for marginal cells in stria vascularis in the guinea pig.