PURPOSE: To compare the results of harmonic ultrasound (US) renal perfusion imaging using 99mTc-DTPA as contrast agent with those obtained when a microbubble contrast medium was used. MATERIALS AND METHODS: Twenty rabbits underwent harmonic US renal perfusion imaging using 99mTc-DTPA as contrast agent, and the imaging procedure was then repeated using a microbubble contrast medium. Three different concentrations of contrast media (200, 300 and 400 mg/ml) and two different scanning techniques (intermittent and continuous) were used, and the images obtained were assessed using six different methods. By means of a computer program, the images were converted to a renal perfusion curve and Tpeak values were calculated. Images obtained after use of the two different contrast media were compared. RESULTS: Tpeak at renal perfusion imaging using 99mTc-DTPA was 6.3+/-0.9 sec, and where microbubble contrast agent was used, the findings were was as follows: 13.8+/-1.6 sec (method 1), 6.5+/-1.1 sec (method 2), 14.8+/-1.7 sec (method 3), 6.6+/-1.0 sec (method 4), 15.2+/-2.0 sec (method 5), 6.4+/-0.7 sec (method 6). Method 6 had the highest correlation coefficients. CONCLUSION: In conclusion, the harmonic ultrasound renal perfusion images acquired using 99mTc-DTPA were similar to those obtained using microbubble contrast agent. Continuous scanning techniques showed correlation.