A catheter for dilating occluded or stenotic blood vessels includes a collapsible filter device disposed between a dilating balloon and the distal end of the catheter. The collapsible filter device comprises a plurality of resilient ribs secured to the catheter at or adjacent the distal end thereof and extending generally axially toward the dilating balloon. Inflation of a filter balloon extends the ribs outward against the vessel wall to stretch filter material secured to the ribs across the vessel to form a cup shaped trap for fragments of a stenosis loosened by the dilating balloon. Upon deflation of the filter balloon, the resilient ribs retract against the catheter to retain the trapped fragments during withdrawal of the catheter. In the preferred embodiment, the ends of the ribs projecting generally toward the dilating balloon are secured to a ring which slides along the catheter. In use, the filter is extended and then the dilating balloon is inflated. Blood flow established by deflation of the dilating balloon carries stenosis fragments into the filter.