The embryotoxicity of ultrasound exposure during pregnancy was investigated in DUB:(ICR) mice. On day 0 of gestation (day of plug), pregnant mice were assigned to one of five groups: cage control, sham exposed (0 W/cm2), 0.05 W/cm2, 0.50 W/cm2, or 1.00 W/cm2. Females were anesthetized on day 8 of gestation and their abdomens were shaved to assure good acoustic coupling. The animals were strapped on a lucite board and placed vertically into a distilled degassed water bath (30°C) so that the abdomen was fully submerged and centered in the axis of the ultrasonic beam. Insonation was carried out using a PZT transducer with a radius of 1.27 cm and a frequency of 1 MHz under continuous wave conditions. Each animal was placed at a distance of 25 cm from the transducer and exposed to the appropriate intensity for 120 seconds. On day 17 of gestation, the maternal animals were killed, the uterine contents were examined, and live fetuses were weighed and then shipped in cold lactated Ringer's solution from Maryland to Arkansas. Fetuses were examined on the day following maternal sacrifice for external and visceral defects and skeletons were prepared and examined subsequently. Slight but significant differences were detected between the cage control and shamexposed groups. No statistically significant changes were seen that could be attributed to ultrasound exposure, although there was a slight increase in the incidence of malformed fetuses and the occurrence of multiple malformations in individual fetuses as intensity of the ultrasonic exposure increased.