Doppler ultrasound is a readily available means of noninvasive evaluation for vascular pathology. This article reviews applications for emergent Doppler evaluation of the native liver and kidneys and renal and hepatic allografts. Doppler ultrasound is useful in the emergent evaluation of the liver and kidney transplant patient. Arterial stenosis, pseudoaneurysm, and venous thrombosis are treatable causes of allograft failure that can be detected easily with color and spectral Doppler. Doppler has a limited but important role in the evaluation of the native liver and kidneys, usually involving prior biopsy or instrumentation.