Abstract: An anti-lock brake device comprises a cylinder adapted to be installed in a pipeline connecting a master cylinder with one or more wheel cylinders of a vehicle. A solenoid-actuated operating member is slidable in the cylinder and is positionable to prevent fluid flow through the device. The operating member is biased into a position in which fluid flow is permitted, energization of the solenoid causing the operating member to prevent fluid flow and, by volume displacement of at least part of the operating member to reduce the fluid pressure on the wheel cylinder side of the device.