Abstract: The present invention relates to catheters and like devices for passage into a body cavity.In the invention the device has a stem portion comprising at least a first tube disposed within a second tube, the tubes being joined at one pair of ends by a flexible member covering the opening of the passage formed between the inner tube and the outer tube. The flexible member is arranged such that the tubes are movable relative to each other and by movement of the inner tube away from or towards the one end of the outer tube the flexible member respectively either can be drawn within the adjacent one end of the outer tube to be enclosed within the outer tube or pushed outside the adjacent one end of the outer tube to expose a balloon. The balloon can be inflated within the body cavity using a fluid under pressure supplied to the balloon from outside the body through said passage.This is a continuation of application Ser. No. 918,506, filed Oct. 14, 1986, now abandoned, which is a continuation of Ser. No.