Abstract: A device for treating human beings or animals, e.g. horses, may be attached to a strap and has a first disc-shaped magnet (1) rotatably mounted on pins (6) within a second annular magnet (3), and held in place by a plate (8). The upper surface of the second magnet (3) is a south pole and the lower surface is a north pole. The first magnet can be rotated through 180 degrees so that its top surface can be chosen to be a north or south pole. The whole device can be removed from its strap and inverted so that different poles can be adjacent the skin in use. A uniform magnetic field of either polarity, or an alternating field can thus be applied to the wearer.