Three improvements to a prior art bioptome are disclosed. The prior art bioptome comprises: tongs, an elongated flexible spiral wire catheter attached to the working end of one of the legs of the tongs; an elongated wire that is rotationally jointed to the working end of the other leg of the tongs and extends axially through the catheter; seals between the inner surface of the catheter and the wire at both ends of the catheter; a pair of hinged jaws one of which is fixed and attached to the end of the catheter and the other of which is movable and is attached to the end of the wire; and a heat-shrunk plastic sleeve about the catheter that sealls the radial exterior surface of the catheter and prevents the catheter from substantial axial expansion. The basic improvement is a heat-shrunk plastic inner sleeve about a segment of the catheter that together with the main sleeve forms a double sleeve about said segment, the inner sleeve having an end that is bias-cut. A further improvement comprises screw fitting the seals between the catheter and wire whereby they are compressed and form a tighter seal against fluid flow into or out of the catheter bore. A still further improvement is a rigid support and guide tube attached to the rotaional joint and extending axially about the elongated wire between the working ends of the tongs.