To see the signal changes in MR angiography (MRA) when occlusions or severe stenoses of carotid arteries occur and to relate these data with the velocity values provided by transcranial Doppler sonography (TCD), 20 patients showing symptomatic or asymptomatic unilateral carotid obstructions underwent both MRA and TCD after digital angiography investigation. No MRA signal was recorded immediately downstream from the carotid occlusion. Low flow velocity values in the carotid siphon and middle cerebral artery (MCA) ipsilateral to the carotid obstruction were associated with altered MRA signals corresponding to the same vessels. Turbulence phenomena induced by reversed flow in the anterior cerebral artery induced MRA signal impairments. In carotid occlusions, there may be a relationship between the MRA patterns and the flow velocity variations detected by TCD, but the two approaches have to be applied together since they provide complementary information.