An ultrasound exposure tank was specifically designed for experimental bioeffects studies. Thirty-six pregnant rats were anesthetized, immersed to the axilla in a water tank, and exposed on Day 15, 17, and 19 of gestation. Twelve rats were exposed to 5.0 MHz pulsed ultrasound of effective pulse duration equal to approximately 0.170 microseconds, pulse repetition rate (PRF) 1 kHz, and a spatial peak, temporal peak intensity (lsptp) of 500 W/cm2, representing a clinically appropriate exposure level. The spatial peak pulse average (lsppa), spatial peak temporal average (lspta), and instantaneous maximum (lm) intensities were determined to be 100 W/cm2, 24 mW/cm2, and 230 W/cm2, respectively. The maximum rarefraction pressure, pr, was measured as 12.5 x 10(5) Pa, and the total power was 2.5 mW. Twelve other rats were exposed to 1500 W/cm2, lsptp, and 12 were sham insonified. Since the focal area was about 0.05 cm2, computer controlled stepper motors moved the rats through the ultrasound field to ensure uniform exposure of the abdominal/pelvic region. Total exposure time was 35 min. A miniature thermocouple was implanted in a few rats to verify that no significant temperature increase took place due to exposure. A total of 278 offspring were maintained until postnatal Day 60 when they were subjected to two of four behavioral tests in random order within sexes. The results indicate no consistently observed dose-related alterations in adult behavior due to prenatal fetal exposure to 5.0 MHz ultrasound below an intensity (lsptp) of 1500 W/cm2.