Abstract: A hydraulic braking system with slip control, comprising a working piston guided within the brake pressure generator, a booster piston of a hydraulic brake force booster for actuating the working piston at least one wheel brake connected to the brake pressure generator and an electrically excitable auxiliary pressure source adapted to be connected to the brake force booster, a control and regulating electronic unit for detecting the wheel rotating pattern and for controlling the wheel braking pressure by pressure modulating valves. An electronic sensor is provided for detecting the relative movement between the pressure rod and the booster piston, the output signals of which are capable to influence the excitation of the auxiliary pressure source. This will permit the brake force boosting, if need be, to be effected independently of actuation forces put in manually, with anti-locking control/traction slip control functions being readily exercisable at any time.