Ultrasound (US) contrast agents containing microbubbles enable color Doppler (power Doppler) ultrasound to detect blood flow in renal masses with greater sensitively and show blood flow and hemodynamics in tumor tissue in solid renal masses. These contrast methods can even detect slow or trapped blood flows by capturing harmonic and pseudo-Doppler signals (loss of correlation). This new method makes it possible to evaluate arterial blood flow in the early (vascular) phase and perfusion blood flow in the late (parenchymal) phase in renal tumors, as is now possible with contrast dynamic CT. Microbubble time intensity curves (TIC) from the region of interest (ROI) can also be derived from this data. Pattern classification may prove useful in characterizing renal tumor tissue. The limited quantity of data based on intensity curves suggests that the time intensity curve may prove useful as a differentiating tool. In addition, such data should enable us to determine the saturation time of microbubble contrast agents, that is, the time required for blood to fill a renal mass, by measuring the minimum intermittent ultrasound emission time necessary to destroy the microbubbles in it. This could enable us to differentially diagnose renal masses of various histologic types. We have already established methods for differentially diagnosing between renal cell carcinoma (N=20) and renal angiomyolipoma (AML) (N=6). Filling times in renal cell carcinoma averaged 4.2賊2.2 seconds in renal cell carcinoma and 21.5賊8.4 seconds in renal angiomyolipoma (significant difference, P=0.004). We have also found that renal cell carcinoma derived from acquired cystic kidneys frequently occurred in patients under long-term maintenance hemodialysis were more easily detected with this method than with CT or MRI. This overview of the principle of conventional color Doppler imaging and our experience using the most recent contrast harmonic ultrasound imaging technology to study renal tumors allows us to suggest that contrast harmonic imaging holds promise as a developing diagnostic method and that further development is warranted.