Abstract: A brake-slip-controlled brake system with a brake-pedal-operated master cylinder (2) assisted by auxiliary energy, with valves (42 through 45 and 66 through 69) in the pressure medium supply lines (40, 41) from the master cylinder (2) to the wheel brakes (10, 17, 38, 39). An electronic circuit configuration is provided for generating valve control signals, and with valves (11, 53, 57, 58, 61, 56) for the supply of pressure medium from the booster chamber (25) into the working chambers (8, 15) of the master cylinder (2). An intermediate piston (18) is sealingly guided in a separate pressure chamber (24) and is arranged between the booster piston (21) and the piston (7) of the master cylinder (2). The pressure chamber (24) is connectible with the return line (48, 76) by way of a check valve (53). The intermediate piston (18) is coupled with the booster piston (21) and it acts on the piston (7) of the master cylinder (2).