Abstract: A co-axial filtering device for removing particles from arteries and veins comprises an outer catheter that can be inserted into a blood vessel and an inner catheter with a filter at its distal end. The filter is a radially expandable receptacle made of an elastic mesh structure of spring wires or plastic monofilaments. The filter expands into engagement with the walls of the blood vessel when it is pushed from the distal end of the outer catheter. A syringe is attached to the proximal end of the inner catheter and particles entrapped within the filter are aspirated through the inner catheter into the syringe. When filtering is no longer necessary, the filter can easily be removed by pulling the elastic material through the outer catheter.