Abstract: A non-contaminating catheter includes a hollow tube having an axial lumen extending along the length thereof, and an elongated, tubular, flexible membrane disposed within the lumen. The leading end of the membrane is circumferentially folded back over the leading edge of the tube and fixed to a guide assembly. As the catheter is inserted into a patient, the membrane is drawn through the tube and out the leading edge of the tube. Once the catheter is fully inserted, the membrane circumscribes the tube; thus, contact between the tube and the patient is substantially, if not entirely, prevented during insertion of the catheter over the length of the membrane. More particularly, the membrane is laid out as the catheter is urged along the anatomical canal and thus remains interposed between the exterior wall of the catheter and the patient's internal organs (e.g., the urethra).