Method for operating a brake system for motor vehicles, which can be controlled in a "brake-by-wire" operating mode both by the vehicle driver and also independently of the vehicle driver, with • hydraulic wheel brakes • a brake master cylinder having at least one pressure space, with the pressure in which at least the wheel brakes of a front axle of the motor vehicle, in particular all the wheel brakes (8, 9, 10, 11), can be supplied in a fall-back operating mode, • a pressure medium reservoir, • a brake pedal for actuating the brake master cylinder, • brake circuits (I, II), which have brake master cylinder and wheel brake pressure spaces and hydraulic connections, • an electrically actuable isolating valve (21a, 21b) for each brake circuit (I, II) for dividing the brake circuit into a brake circuit section (22a, 22b) which can be subjected to pressure by the vehicle driver and a brake circuit section (12a, 12b) which can be subjected to pressure "by wire", • an electrically actuable inlet valve (6a-6d) and an electrically actuable outlet valve (7a-7d) for each wheel brake for setting wheel-specific brake pressures, • an electrically controllable pressure and volume setting device, • an electrically actuable connection valve (30a, 30b), in particular a valve of this kind which is closed when deenergized, for each brake circuit (II, I) for hydraulic connection of the electrically controllable pressure and volume setting device to the brake circuit section (12a, 12b) which can be subjected to pressure "by wire", • a simulation device, which can be connected hydraulically to at least one pressure space of the brake master cylinder and can be activated by means of an electrically or mechanically actuable simulator enable valve, having a preset characteristic, and which gives the vehicle driver a pleasant brake pedal feel in the "brake-by-wire" operating mode, and • an electronic open- and closed-loop control unit, in particular for controlling the pressure and volume setting device, the isolating valves (21a, 21b), the connection valves (30a, 30b), the simulator enable valve and the inlet and outlet valves (6a-6d; 7a-7d), characterized in that, to set wheel-specific brake pressures, the inlet and outlet valves (6a, 6d; 7a-7d) are controlled in an analog manner by being supplied with different electric currents in order to allocate a pressure medium volume flow made available by the pressure and volume setting device to the wheel brakes having a requirement for a change in pressure, wherein the electrically controllable pressure and volume setting device is used to displace pressure medium volumes which are proportioned according to the desired changes in wheel brake pressure and, by means of the different control currents of the inlet and outlet valves (6a-6d; 7a-7d), are passed to the selected wheel brakes as an inlet flow or out of the wheel brakes selected for a pressure reduction as a volume discharge flow. • hydraulic wheel brakes • a brake master cylinder having at least one pressure space, with the pressure in which at least the wheel brakes of a front axle of the motor vehicle, in particular all the wheel brakes (8, 9, 10, 11), can be supplied in a fall-back operating mode, • a pressure medium reservoir, • a brake pedal for actuating the brake master cylinder, • brake circuits (I, II), which have brake master cylinder and wheel brake pressure spaces and hydraulic connections, • an electrically actuable isolating valve (21a, 21b) for each brake circuit (I, II) for dividing the brake circuit into a brake circuit section (22a, 22b) which can be subjected to pressure by the vehicle driver and a brake circuit section (12a, 12b) which can be subjected to pressure "by wire", • an electrically actuable inlet valve (6a-6d) and an electrically actuable outlet valve (7a-7d) for each wheel brake for setting wheel-specific brake pressures, • an electrically controllable pressure and volume setting device, • an electrically actuable connection valve (30a, 30b), in particular a valve of this kind which is closed when deenergized, for each brake circuit (II, I) for hydraulic connection of the electrically controllable pressure and volume setting device to the brake circuit section (12a, 12b) which can be subjected to pressure "by wire", • a simulation device, which can be connected hydraulically to at least one pressure space of the brake master cylinder and can be activated by means of an electrically or mechanically actuable simulator enable valve, having a preset characteristic, and which gives the vehicle driver a pleasant brake pedal feel in the "brake-by-wire" operating mode, and • an electronic open- and closed-loop control unit, in particular for controlling the pressure and volume setting device, the isolating valves (21a, 21b), the connection valves (30a, 30b), the simulator enable valve and the inlet and outlet valves (6a-6d; 7a-7d),