Abstract: A device for temporarily or permanently closing body passages or cavities in humans and animals and including a member (2) of a material which swells at least 20% by absorbing body fluids and which is substantially inert to body fluids and surrounding tissues, the member (2) being dimensioned so as to be able to be introduced with clearance into the passage or cavity in its unswollen state but to take up the whole cross-section of the passage or cavity in the swollen state and then to be held by pressure against the surrounding walls of the passage or cavity.