A series of experimental studies using a test phantom carried out to compare the basic characteristics of phase inversion tissue harmonic imaging (THI) and conventional sonography (CUS) clearly showed the superiority of tissue harmonic imaging over conventional sonography. Tissue harmonic imaging had higher axial, lateral, and contrast resolution and fewer side-lobe artifacts. Brightness measured to analyze the intensity of harmonics generated by hepatocellular carcinomas (HCC), hepatic hemangiomas, and gall stones in clinical cases clearly showed that hyperechoic hepatocelluar carcinomas, hepatic hemangiomas, and pure cholesterol stones generated more harmonics than adjacent background liver tissue. The brightness of hypoechoic or isoechoic hepatic hemangiomas was significantly increased on tissue harmonic imaging, while that of both hypoechoic and isoechoic hepatocellular carcinomas was not. Sensitivity and specificity in diagnosing hepatic hemangiomas were 81.3% and 79.2%, respectively. Likewise, the brightness of pure cholesterol stones, but not that of other gallstones, was significantly increased on tissue harmonic imaging: sensitivity and specificity for pure cholesterol stones were 100％ and 78.4％, respectively. These results indicate the usefulness of phase inversion tissue harmonic imaging in the tissue characterization. The next series included 502 cases with 570 abdominal nodules. We visualized each lesion at the same slice with both conventional sonography and tissue harmonic imaging and compared their image quality and rate of detection by depth of lesion. Rates of improvement were 89.7％, 91.8％, and 83.9％ in shallow, middle, and deep lesions, respectively. Respective rates of detection of new lesions were 5.7％, 7.0％, and 3.6％. Phase inversion tissue harmonic imaging visualized all lesions examined more clearly than conventional sonography, regardless of location. We thus suggest that phase inversion tissue harmonic imaging will replace conventional sonography as a screening method.