Purpose: To compare, in terms of their feasibility and normal range, $^{99m}$Tc-DTPA renal perfusion imaging and renal perfusion imaging using harmonic ultrasound (US)with a microbubble contrast agent for the evaluation of renal perfusion after renal transplantation. Materials and Methods: During a six-month period, thirty patients who had received a renal transplant underwent both $^{99m}$Tc-DTPA renal perfusion imaging and renal perfusion imaging using harmonic US with a microbubble contrast agent. Sonographic renal perfusion images were obtained before and after a bolus injection of the microbubble contrast agent Levovist$^{TM} (SH U 508A; Schering AG, Berlin, Germany) every 3 seconds for 3 minutes. Sonographic renal perfusion images were converted into a renal perfusion curve by a computer program and Tpeak of the curve thus obtained was compared with that of the $^{99m}$Tc-DTPA curve. Results: Average T$_{peak}$ of the $^{99m}$Tc-DTPA renal perfusion curve was 16.2 seconds in the normal group and 39.6 seconds in the delayed perfusion group, while average T$_{peak}$ of the sonographic renal perfusion curve was 23.7 seconds and 46.2 seconds, respectively. T$_{peak}$ of the sonographic renal perfusion curve showed a good correlation with that of the $^{99m}$Tc-DTPA curve (correlation coefficient=0.8209; p=0.0001). The cut-off value of T$_{peak}$ of the sonographic renal perfusion curve was 35 seconds (sensitivity=90%, specificity=95%). Conclusion: In patients who have received a renal transplant, the findings of renal perfusion imaging using harmonic US with a microbubble contrast agent show close correlation with those of $^{99m}$Tc-DTPA renal perfusion imaging. The optimal cut-off value of Tpeak of the sonographic renal perfusion curve was 35 seconds