Although Doppler and color Doppler ultrasonography has been used extensively to examine acute changes in renal allograft function, there have been few reports on the role of Doppler ultrasonography in the assessment of chronic rejection. In those studies that have addressed chronic rejection, there is agreement that changes in renal function are not accompanied by consistent changes in flow waveform shape. The pathology of chronic rejection may be very different from the changes seen in acute rejection and its onset is usually gradual. Some authors have suggested that the decline in function is accompanied by lower Doppler frequency shifts (corresponding to lower velocities) in intra-renal arteries. In a preliminary study comparing grafts with normal renal function and with biopsy-proven chronic rejection, it has been shown that for grafts with chronic rejection, observed intra-renal velocities are lower, especially at segmental and interlobar levels. This may be a more reliable reflection of reduced renal blood flow in chronic rejection than conventional Doppler ultrasound analysis of flow waveform shape. However, the diagnostic use of changes to intra-renal flow velocities in chronic rejection is currently very limited. 0 1992 John Wiley & Sons, Inc. Indexing Words: Doppler ultrasonography * Color Doppler ultrasonography * Renal transplants * Transplant rejection e Kidney transplant ,