The present invention relates to a method for the preparation of a treatment machine for the treatment of a medical liquid comprising a coupling surface with actuators, with a cassette comprising a hard part with liquid-conducting passages which are covered by a flexible film being able to be coupled to the coupling surface of the treatment machine so that the actuators can control the liquid flow in the liquid-conducting passages by pressing the flexible film down into the cassette. In this connection, a switch is made after the setting up of the treatment machine and before the start of treatment into a stand-by mode in which the actuators are alternately moved to relieve the flexible film. It is possible for the first time by the stand-by mode before the start of treatment in accordance with the invention to completely uncouple the time-consuming setting up of the treatment machine from the treatment itself in a time aspect. The present invention furthermore comprises a corresponding treatment machine having a control for the carrying out of the method in accordance with the invention.