Abstract: A hydraulic servo-brake arrangement for a vehicle brake system having two brake circuits comprises a piston-cylinder arrangement with a piston rod for connection to the vehicle brake pedal and with a cylinder inlet from a fluid reservoir and a cylinder outlet to a first brake circuit, and a regulator valve with an inlet from a pressure source and an outlet to a second brake circuit. The pressure in the first brake circuit influences the regulator valve to open the connection between the pressure source and the second circuit, while the pressure in the second circuit urges the piston in the braking direction. The piston is mounted for limited displacement in relation to the piston rod, whereby valve control means are movably mounted together with the piston rod to urge the control valve in the opening direction after a predetermined piston rod travel in the braking direction.