The purpose of this study was to develop an animal model that could be used to test the ability of Doppler ultrasound to detect arterial emboli composed of materials that are often involved in cerebral emboli. Emboli introduced into the rabbit aorta via the left renal artery consisted of clotted whole blood, platelets, atheromatous material, fat, or air. The ultrasound examination was carried out continuously during the studies using a multifrequency transcranial Doppler apparatus with a 2-MHz probe, a sample volume of 15 mm, at a depth of 15 mm. The intensity of the Doppler spectrum was measured and displayed as a 15-shade color scale, each shade representing a 3-dB difference. The diameter of the aorta at the site of the ultrasound examination was similar to the diameter of the middle cerebral artery in humans. All 125 emboli introduced were clearly detected because they caused a Doppler signal at least 15 dB greater than that of the surrounding blood. These results show that the potential for emboli detection using Doppler ultrasound in the clinical situation is now considerable.