Echo-enhancing agents improve the signal intensity of transcranial Doppler signals, enabling a novel approach of three-dimensional transcranial vascular imaging by Doppler ultrasound. The basic principle, system requirements and early clinical results with a custom built system are described. Transcranial color Doppler imaging was performed through the temporal bone acoustic window. During i.v. administration of the transpulmonary stable, galactose-based echo-enhancer Levovist (Schering) the video output of the ultrasound scanner was digitized and the spatial position of the recorded frames was simultaneously registered using a mechanical position sensor. After automatic segmentation of the color information, the 3D datasets were reconstructed offline using a Unix-based workstation (Silicon Graphics). Visualization was achieved by maximum intensity projection or surface visualization techniques. Administration of Levovist resulted in good enhancement of the vascular Doppler signal intensity, enabling acquisition of a 3D dataset of the complete circle of Willis with an imaging window of approximately 3-5 min for one i.v. injection. The vascularity of tumors could be recorded as a 3D dataset and further analyzed. The power Doppler technique with echoenhancement proved a valuable tool for 3D dataset recording. 3D datasets clearly facilitated the diagnosis of the vascular anatomy and lesion vascularity and provided additional information on localization of feeders, vascular displacement and extent of tumor vascularity.