PURPOSE: To determine the value of high resolution ultrasonography (US) for the detection of hepatocellular carcinoma in the HBx transgenic mice. MATERIALS AND METHODS: Forty-two HBx transgenic mice aged 8-20 (mean, 14) months underwent high-resolution ultrasound using a 10 -12 MHz linear transducer. US findings indicating the presence or absence, number, size and echogenicity of each hepatic tumor were analyzed, and inaddition, color or power Doppler US was used to analyse tumoral vascularity. In each animal, sacrificed less than five hours after US examination, sonographic and pathologic findings were correlated. RESULT: On gross pathologic examination, 20 hepatocellular carcinomas measuring 1.5 -15 (mean, 4.7) mm in diameter were found in 16 mice; US revealed that 17 of the tumors were homogeneous hypoechoic nodules. With regard to tumor detection, sensitivity was 85%, specificity 96%, positive predictive value 0.944, negative predictive value 0.897, and overall accuracy 90%. Doppler US revealed that in three nodules, intratumoral vessels were present. Inthe other 26 mice, gross examination showed that no mass was present; microscopically, however, four nodules measuring 0.3 -1.2 mm were found in four of these animals. Tumoral vascularity detected by color Doppler US corresponded to the intratumoral vessel within the nodules. One peritoneal nodule, confirmed as a metastatic tumor, was found at the greater omentum. CONCLUSION: In HBx transgenic mice, high-resolution US is valuable for the detection of hepatocellular carcinoma.