Diagnosing calf vein thrombosis (CVT) by color Doppler ultrasound (US) is often a difficult task because of swelling or obesity. The purpose of this study was to assess if IV infusion of Levovist can improve the accuracy and reduce the rate of indeterminate examinations. A total of 20 patients with suspected CVT underwent color Doppler US without and with Levovist followed by ascending venography as the "gold standard," which detected calf clots in 7 patients (35%). Compared to routine noncontrast sonography, Levovist examination reduced the rate of indeterminate scans from 55% to 20% and improved the specificity for the detection of CVT from 25% to 67% without compromising sensitivity (100% to 86%) notably. Image quality was improved in 13 (65%) of 20 scans. In conclusion, we can say that Levovist improves the quality of duplex examination of the calf veins, especially in cases with difficult conditions due to obesity or swelling.