The invention relates to a brake system for motor vehicles, which can be controlled both by a driver and independently of the driver in a "brake-by-wire" operating mode, comprising a brake pedal (1), at least two wheel brakes (8, 9, 10, 11) that can be actuated hydraulically, a first and a second brake actuation sensor (505a, 505b), a first electrically controllable pressure source (301, 5), by means of which the wheel brakes can be actuated, a first electronic control unit (112, 12), which is connected to the first brake actuation sensor (505a) and controls the first pressure source (301, 5), a second electrically controllable pressure source (302, 249), by means of which the wheel brakes can be actuated, a second electronic control unit (139, 39), which is connected to the second brake actuation sensor (505b) and controls the second pressure source (302, 249), a hydraulic control device (300), which comprises, in particular, at least a first solenoid valve (26, 26a, 26b) between the wheel brakes and the first pressure source and a second solenoid valve (23, 23a, 23b) between the wheel brakes and the second pressure source, and a data connection (53) between the first electronic control unit (112, 12) and the second electronic control unit (139, 39), wherein the first electronic control unit (112, 12) has a first interface (601) and the second electronic control unit (139, 39) has a second interface (602), wherein the first interface and the second interface are not connected to each other.