A catheter (1) for insertion into a body cavity of a subject (such as the urinary bladder), and having a drainage tube (2) extending from a drainage opening (3) adjacent a distal end (4) of the catheter to a drainage outlet adjacent a proximal end of the catheter； a closure member (7) mountable for sliding movement within the drainage tube between a first position such that said drainage opening is in fluid communication with the drainage outlet and a second position wherein the closure member blocks fluid communication between the drainage opening and the outlet port； and an actuator (18), operable from the proximal end of the catheter, to move the closure member between the first and second positions. The closure member can comprise a second tube, sliding within the drainage tube, or a slideable plug.
