MES are ultrasound signals, which result from the passage of embolic material through an insonated vessel. MES are used for optimization of operation techniques, recognition of re-thrombosis after carotidendarterectomy and estimation of the embolic risk of stenoses of brain-supplying vessels. By means of this study a new method for detection of MES was enhanced and tested. For this an additional sample volume was placed in the brain parenchyma. We hypothesized, that artefact signals can be detected in both sample volumes, whereas MES can only be detected inside the vessel. On the basis of intensity measurements we calculated an optimal cut-off by means of receiver operating characteristic curves to discriminate microembolic and artefact signals. This cut-off is 27% loss of intensity between both sample volumes, and it was tested by application in various patient groups. All together we evaluated 1858 MES und 1957 artefacts, and we were able to identify 95,7 and 97,9% respectively. Promising results could be achieved, and further evaluation of this method is warranted.