A method for delivering a drug to the site of an intravascular occlusion. A guidewire having a balloon at one end is advanced across the occlusion using a guide catheter, and the balloon is inflated distal to the occlusion to occlude the blood vessel. An aspiration catheter is then inserted into the vessel with its tip less than about 5 mm from the surface of the balloon, and a drug is delivered which flows distal to proximal to treat the occlusion.