Abstract: A guidewire threader to facilitate insertion of the proximal end of a guidewire into the distal end of a catheter including two clamping pieces each of which has the shape of a lever having two arms and are hinged to each other for pivoting about a common axis between a closed clamp position and an open release position. A spring maintains clamping surfaces, each of which is provided on one arm of each clamping piece, positively in contact with each other in the clamp position. The clamping surfaces in their condition in contact with each other define a passage oriented roughly parallel to the common pivot axis open at both ends, the passage containing a section having an interior dimension corresponding to the outer diameter of the catheter and which is flared funnel-shaped at both of its ends. In the release position, the clamping surfaces open the passage in the lateral direction for removal of the guidewire.