Pathologic flow profiles in renal arteries can be found in cardiovascular and renovascular disease. Obstructions of the left hart (aortic stenosis, hypoplastic left heart syndrome, coarctation of the aorta) cause diminished flow with low peak systolic velocities. In renal arteries of infants with leakage of the aortic "Windkessel" (persistent ductus arteriosus, truncus arteriosus communis etc.) a low diastolic amplitude can be found. Significant left-to-right shunts can lead to a diminished or even retrograde diastolic flow. In renal artery stenosis a high velocity jet with spectral broadening can be found in the region of the stenosis. Distal to the stenosis low blood flow velocities can be shown. In renal vein thrombosis the obstruction of the peripheral vessels cause a missing or even negative diastolic flow in the renal arteries, whereas venous blood flow is diminished or even missing. Kidney diseases with swelling of the organ (acute rejection of a transplanted kidney) can cause diminished, missing or even retrograde diastolic flow in the renal arteries dependent on the severity of the edema. These alterations can be used for the early diagnosis of acute rejection which offers the opportunity for early and efficient therapeutic management.