Abstract: In a slip-controlled brake systems which provide for a hydraulic resetting of the brake pedal in the event of slip control, it must be ensured that the change-over valves which check the connection between resetting chamber and compensating reservoir are open in their initial position. Otherwise brake application is blocked. In the disclosed anti-lock brake system, the actually developing pressure or fluid flow is compared by a pressure sensor or flow sensors during a test cycle with the pressure or flow to be expected when the valves are open.