a method and apparatus for applying a polymer coating on an elongated substrate , preferably an elongate intracorporeal device in the form of a guidewire . an extrudable polymer cartridge is moved by a cartridge advancement mechanism into a guide chamber which is heated at an end with a die or orifice through which a desired portion of a guidewire may pass and be coated . parameters such as guide chamber temperature , pull speed and force exerted by the cartridge advancement mechanism may be controlled with a computer program in order to achieve repeatable results . the guide chamber , extrudable polymer cartridge , die , and push tube may all be made from polymer components which can be reused or disposed of after a single use . the extrudable polymer cartridge may have a variety of configurations including multiple layers of different materials , eccentric shapes , multiple lumens for multiple elements to be drawn through and coated and asymmetric disposition of different materials with respect to the longitudinal axis as viewed in a transverse cross section which can give bending properties having a preferred direction in the coated guidewire or device .