PURPOSE: To evaluate the usefulness of US with contrast agent on breast tumors. MATERIALS AND METHODS: Fifteen breast tumors in fourteen patients underwent color Doppler US before and after intravenous injection of a microbubble contrast agent (Levovist(r), Schering AG, Berlin, Germany). Benign le-sions were 8 and malignant lesions were 7 among these. Real-time power Doppler ultrasonographic images were recorded on a videotape and representative images were color-printed. Tumor vascularity was analyzed on real-time images in regard to its presence or absence, and changes in diameter and number of vessels, presence or absence of blush around the vessels. Two observers reached a consensus. Results of malignant tumors were compared with those of benign tumors. RESULTS: Color Doppler signal intensity increased in 12 of 15 cases (80%). Number of vessel increased in 9 of 15 cases (60%) and diameter of vessel increased in 12 of 15 cases (80%). Vascular blush around the enhanced ves-sel was present in 5 of 15 patients (53%). Color Doppler signal increased in 5 of 8 benign lesions (63%) and 7 of 7 malignant lesions (100%). Number of vessel increased in 4 of 8 benign lesions (50%) and 5 of 7 malignant le-sions (71%). Diameter of vessel increased in 5 of 8 benign lesions (63%) and 7 of 7 malignant lesions (100%). Blush around the enhanced vessel was present in one of 8 benign lesions (13%) and 4 of 7 malignant lesions (57%). The time to peak enhancement was shorter in malignant cases (mean = 45 sec) than benign cases (mean = 82 sec) CONCLUSION: US with contrast agent on breast tumors is effective to detect blood flow within the mass and may be helpful to differentiate malignant from benign lesions.