To test the safety and efficiency of commercially available thrombectomy catheters in clearing simulated internal carotid artery (ICA) thrombosis.Comparative in vitro study.A model of the ICA was filled with human thrombus, the 'circle of Willis' back pressure was set at either 10 or 30 cm of water. Five thrombectomy devices (Hydrolyser, Clot Buster, Acolysis System, AngioJet and Fogarty embolectomy catheter) were compared for (i) efficiency at removing thrombus, (ii) pressure changes at the tip of each device, and (iii) distal embolisation by flow cytometry.Thrombus clearance was greatest with the AngioJet (median 95%, range 92-97%) and least with the Acolysis System (median 34%, range 12-50%). The Clot Buster and Hydrolyser were safest as they produced only negative tip pressures, the AngioJet and Balloon catheter produced positive and negative pressures risking distal embolisation. The Acolysis system produced no pressure change during use. Distal embolisation (of particles between 5 and 40 microm diameter) was greatest with the Fogarty balloon catheter at 10 cm water (P<0.05) and least with the Hydrolyser and Clot Buster.Balloon embolectomy for ICA thrombosis risks further embolic cerebral damage. The Hydrolyser and the Clot Buster show the greatest promise for ICA thrombectomy.