The authors studied the effect of transcranial ultrasound on patients with acute middle cerebral artery occlusion and contraindications for thrombolysis. Fifteen consecutive subjects were randomized for insonation over 1 hour or for inclusion in a control group. By day 4, recanalization and neurologic improvement occurred more frequently in the target group. Ultrasound-induced acceleration of clot dissolution may be an option for patients with contraindications for recombinant tissue plasminogen activator.