The invention relates to a
brake system for motor vehicles, comprising a master
brake cylinder (2), to each of the two pressure chambers of which a
brake circuit (I, II) with wheel brakes (8, 9, 10, 11) can be connected or is connected, an electrically actuatable block valve (23a, 23b) for each brake circuit (I, II) for separating the pressure chamber (17, 18) from the brake circuit, a first electrically controllable pressure supply unit (5), an electrically actuatable sequence valve (26a, 26b) for each brake circuit (I, II) for hydraulically connecting the first pressure supply unit (5) to the brake circuit, and a
simulation unit (3) which can be hydraulically connected to at least one pressure chamber (17) of the master brake cylinder (2) by means of a simulator release valve (32), wherein a second electrically controllable pressure supply unit (49, 149) having at least one intake port and a pressure port is provided, the intake port of which is connected or can be connected to one of the pressure chambers (17, 18) and the pressure port of which can be connected or is connected to the brake circuit (I, II) associated with the pressure chamber. The invention further relates to a method for operating a brake
system.