Abstract: A hollow, open-ended sheath is removed from a position enclosing a catheter which has been inserted through the sheath with a close tolerance and introduced into a human body thereby. A cutting blade is mounted in a deforming and guiding mechanism connected to the blade and engageable with the sheath for exerting pressure on the sheath in such a manner as to deform the sheath away from the catheter at a point immediately adjacent to the cutting blade and into contact with the cutting blade while maintaining the catheter beyond the reach of the blade. The device guides the blade for lengthwise movement relative to the sheath. The blade cuts the sheath in a lengthwise direction for removal from the catheter while the catheter remains in place.