A system for positioning a catheter includes a nerve stimulator needle carried within the lumen of the catheter. A microelectrode is configured as a needle tip precisely protruding beyond a tapered distal end of the catheter. The catheter and needle are fixed against axial movement relative to one another to maintain the precise configuration of the microelectrode needle tip conductive surface by a releasable clamp which is grasped by the practitioner to compress the catheter lumen against the needle without permanent deformation of the needle shaft while simultaneously advancing the needle and the catheter toward a target nerve.