The cochleae of 51 guinea pigs were exposed to focused ultrasound of 1.25 megacycles. The ultrasonic probe, with a tip area of 1.8 mm2 was gently positioned against the otic capsule at the third coil from the base for 3 minutes at an intensity of 20 W/cm2. The only variable factor in this study was the survival time which was selectively set between 12 hours and 2 months. The stria vascularis was stained by the peroxidase-benzidine method. Circumscribed lesions of rather uniform character were found. The acute changes consisted of vascular constriction, thrombus formation, disruption and extravasation of blood. After survival times of one and two months, all vessels within a small segment of the spiral ligament and the stria vascularis had disappeared. No definite signs of revascularization of the target area were observed. Most of the pigment granules of the stria vascularis were dissolved within the treated zone. The effects of focused ultrasound and argon laser irradiation upon the vessels in the lateral wall of the cochlear duct have been compared.