Contrast ultrasound is a promising and straightforward method that is superior to established sonographic techniques such as conventional B-mode scanning which is used for volume measurement and hematoma demonstration. Color Doppler is important for the evaluation of rejection, the detection of perfusion defects, and complete vascularization in the diagnostic evaluation of kidney grafts. Moreover, contrast US has the potential for tumor characterization in transplanted kidneys. A single examination by contrast ultrasound can answer a variety of questions with respect to the early postoperative phase and chronic damage. New applications of contrast US will arise from the further technical development of ultrasound equipment. The rapid technical advances seen in recent years have been followed by the introduction of new software tools for the analysis of raw datasets or the improved visualization of microbubbles at very low energy. Initial studies show that efficient and early diagnosis of rejection is possible. Surgical complications like perfusion defects or hematoma can also be identified.