Abstract: A catheter introducer which allows a dilator member and a sheath member to be engaged with and disengaged from each other promptly and smoothly. The catheter introducer includes a sheath member consisting of a sheath portion and a sheath hub and a dilator member consisting of a dilator portion and a dilator hub and a locking mechanism operatively connecting the sheath member and dilator member during the insertion of the catheter introducer into the body of the patient. The dilator hub includes one or more flange members associated therewith and the flange member is rotatable with respect to the sheath hub to selectively engage the sheath hub in a first position and disengage the sheath hub in a second position.