Abstract: Stunning of animals to be slaughtered at slaughterhouses takes place by exposing the animals for a sufficiently long period of time to an anaesthetic atmosphere, such as an atmosphere of carbon dioxide. A number of animals is first driven into a transport box (2b) which has been placed in a filling area at the slaughterhouse. Then a filled box is transported to a waiting area for boxes (2c), and from this waiting area a box is taken when needed and led through a stunning area (3) filled with the anaesthetic atmosphere, such as an oblong pit with room for 2-15 boxes (2d), which are led in one after another. The boxes (2f) with stunned animals are emptied of animals to be slaughtered, which are chained, whereas the empty boxes (2a) are returned to the filling area for renewed use. The removal of a box (2c) from the waiting area and the supply to the stunning area (3) are controlled by the current slaughtering speed and the number of boxes (2d) in the stunning area.