Abstract: The invention relates to a method for introducing a tube (3) in order to deliver or remove substance(s) at positions in the gastrointestinal tract by letting a human subject or an animal swallow a firm body (1), the "bead part", to which said tube is fastened and letting the head part (1) be moved by peristalsis to desired positions. According to the invention, said head part (1), which is provided with a bore (2) or cavity running through it and being in fluid connection with said tube (3), is halted at a selected position in any part of the gastrointestinal tract by fixing the tube at the entrance into the body or outside the body. Said tube (3) is marked to indicate length of the swallowed part of the tube in order to guide the finding of said selected position. Liquid or gas is delivered or aspirated through said tube (3) and said bore (2) or cavity running through the head part (1).