Method for the aseptic filling of a bag with a pharmaceutical product or liquid which comprises the following steps: a) a first step in which the cap is inserted in the inlet of the bag； b) a second step in which said cap is raised and the pharmaceutical product or liquid concerned is introduced； c) a third step in which the cap is re-inserted in the inlet of the bag； and d) a fourth step in which the cap and the inlet of the bag are welded.
