The invention discloses an apparatus for removing samples or introducing fluids from/into system(s) having flexible walls. A sampler/fluid dispenser (3) is fixed on the outside with a connecting area (4) of its base (5) on a sample removal region/fluid dispensing region (6) of the flexible wall (2) and, in its interior, has a severing element (8). At least the severing element (8) can be pushed forward in the direction of the sample removal region/fluid dispensing region (6) in order to remove the samples and in order to introduce fluids, in such a way that the wall (2) can be perforated within the sample removal region/fluid dispensing region (6). The system (1) comprises containers, bags or tubes for filling, mixing, transporting, storage of media, such as biological liquids, sera, buffers, ultra-pure water and can be used as biological reactors or cell culture vessels in the pharmaceutical and biotechnical industry.