A method for reducing distal embolization during insertion of devices to treat plaque, thrombi and other intravascular occlusions. Using a guide catheter, a guidewire is delivered to a site proximal to the lesion. An aspiration catheter is then introduced over the guidewire, and the two are moved together in a distal to proximal direction across the occlusion. The aspiration catheter is then moved in a proximal to distal direction while continuously aspirating, which prevents embolization of any particles which may be created during the crossing of the guidewire.