In vivo animal experiments were performed to study the cataractogenic effects of high-frequency, high-intensity ultrasound. A series of anesthetized rabbits was insonified with quantified exposures of ultrasound using a 9.8 MHz focused ultrasonic beam. Ophthalmoscopic and slit lamp examinations revealed small haze cataracts as the 1st stage of lenticular damage. Larger exposures produced totally opaque cataracts. These first appeared as fine white threads surrounded by haze cataracts. The intensity-exposure time conjugates required to produce haze cataracts were determined over times ranging from 35 ms-5 s. At short times (under 100 ms) a relatively constant amount of energy was needed for cataract production. A longer times the required energy progressively increased. This observation, along with the physical appearance of these cataracts, suggested that these lesions are the result of thermal phenomena.