We have so far performed color Doppler echography to make diagnosis in renal transplantation. The ultrasound contrast agent in color Doppler developed and used recently has made possible the recording and measuring of low velocity wave in transplant kidneys. As characteristics of that, mention can be made of improvement in detection of the flow, reliability of assessment of the velocity, space resolving power. It is useful particularly for the peripheral blood vessels on chronic rejection and the interlobar artery on acute vascular rejection. With that put to practical use, imaging diagnosis in the field of renal transplantation has improved in its diagnosing ability and is expected to make further development in the future.