Abstract: Vibration damper, in particular for motor vehicles, including a work cylinder, a work piston fastened to a piston rod and dividing the work cylinder into two work chambers, possibly an equalization chamber and a piston rod guide which seals the piston rod against the atmosphere, whereby the work chambers are filled with a magnetorheological fluid to which an electric coil can be applied. In the event of a failure or malfunction of the electric coil, it must be possible to achieve a safe damping force, by having at least one permanent magnetic field which acts on the magnetorheological fluid.