A 77 year old woman was hospitalized one hour after the onset of right hemiplegia and aphasia. Magnetic resonance imaging (MRI) examination was negative and MRA indicated occlusion of the left middle cerebral artery. Treatment with streptokinase was instituted (a 60 minute intravenous infusion of 1.5 MU of streptokinase in 100 ml of saline solution). Two hours after infusion, the patient's motor function clearly improved. An MRA examination performed six hours later showed partial recanalization of the obstructed vessel. Our report demonstrates the potential usefulness of MRA monitoring during thrombolytic therapy.