A filter useful in tubular organs of the human body, intended primarily for endovascular use during surgical procedures for removal of plaque and other treatment of stenoses in arteries, in order to entrap particles of plaque or other materials freed from the interior wall of an artery while permitting continued flow of blood through the artery during the procedure of treating the stenosis. Several filter elements are fastened in apart-spaced relationship with one another along a flexible elongate member and are large enough to require the entire flow of blood through the artery to pass through the filter elements. An open-mouthed tubular stocking of porous filter material encloses the filter elements and supports the periphery of each filter element. Successive filter elements, progressing in the direction of blood flow, pass only progressively smaller particles. In a preferred embodiment, the mouth of the stocking can be closed to retain particles of material within the filter as it is withdrawn from the artery after repair of a stenosis.