Tensile properties and pressure-diameter-axial force relations of a newly developed small-diameter arterial graft were determined and compared to those of commercially available grafts and natural arteries. The material was synthesized from 4,4'-diphenylmethane diisocyanate, polytetramethylene glycol, and polyethylene oxide, chain-extended with ethylene glycol. Porous conduits (3-mm internal diameter) were fabricated of this material by means of a phase separation technique, and their outer surfaces were covered with woolly polyester net in order to prevent excessive dilation. Mechanical tests indicated that the polyurethane graft has distensibility and strength similar to that of natural arteries, and has been proved to be useful for the arterial reconstruction, particularly for the replacement of small-diameter blood vessels.