Abstract: A hydraulic brake unit for automotive vehicles, with brake slip and traction slip control is furnished with a brake pressure generating assembly (1) with an auxiliary hydraulic pressure supply system comprising a hydraulic pump (5) and an auxiliary pressure modulation valve (6). On the start of the slip control action, an auxiliary hydraulic pressure is generated and the auxiliary pressure supply line (18) connected, instead of the brake pressure generating assembly (1), to the wheel brakes (12 to 15). By means of a 2/2-way valve being normally switched to free passage, the reflux path from the modulation valve (6) to the pressure balancing tank (7) can be shut off. In this manner an auxiliary pressure is generated also when the modulation valve (6) is not subject to any control action, by which auxiliary pressure a pressure can be generated in the wheel brakes (12 to 15) independently of whether a brake actuation takes place or not.