A valve for magnetorheological fluids is formed with a control duct in which the magnetic field of a magnetic device, consisting of a permanent magnet and coil, acts on the fluid. The viscosity of the fluid is directly proportional to the magnetic field strength, with the result that the flow resistance of the valve can be varied via the coil current. The respective control duct is arranged in the end-face region of the coil and runs radially with respect to the center line of the valve, with the result that high flux densities can be achieved in the control duct. A permanent magnet is arranged in the inner space of the coil and, even under currentless operating conditions, can close the valve up to a certain blocking pressure.