According to clinical observations, cardiogenic embolism occurs more often in the anterior than in the posterior cerebral circulation. An ultrasound (US) contrast agent was used to artificially produce microembolic signals (MES) to imitate the intracranial distribution of systemic emboli. Systemic microemboli were simulated by IV administered US agent (Levovist(R) 300 mg/mL as bolus). A total of 20 patients were monitored by means of transcranial Doppler sonography (TCD), 3 min after the injection, with a 2-MHz transducer simultaneously at 50 mm (middle cerebral artery, MCA, on one side) and 90 mm (basilar artery, BA). Four 3-min recordings were done (two of the right MCA, two of the left MCA, with the BA, respectively). Three observers and an automatic detection system independently performed an off-line analysis. A total of 160 recordings were analyzed. The mean numbers of detected high-intensity transient signals (HITS) were 34.5 +/- 28.2 in the right MCA (simultaneously registered HITS in the BA: 9.4 +/- 16.8) and 39.1 +/- 34.2 in the left MCA (simultaneously registered HITS in the BA: 12.2 +/- 14.5). Only 21.4 to 23.7% of all HITS were recorded in the BA. Microembolic signals artificially produced by means of US contrast agent made it possible to mimic the physiologic distribution of small embolic particles. In future, these might help to investigate the distribution of systemic emboli in different vascular territories in various pathologic conditions of the cerebral blood flow.