In orthodontic treatment, the use of mechanical forces generated by magnetic fields have increased significantly over the past years, triggered by the introduction of rare earth permanent magnetic alloys. Rare earth magnets, initially made from cobalt-samarium alloy and later from neodymium-iron-boron alloy generate high mechanical forces in relation to their small size. Relating to their use in orthodontic treatment, queries about possible side effects have been expressed. This study was undertaken in order to determine if cell growth and attachment in vitro is affected over time in a static magnetic field of a magnitude comparable to that used clinically. Significantly and progressively impaired attachment and growth over a 5 week period was observed when human periodontal fibroblasts were cultured in a static magnetic field. These results indicate that a static magnetic field itself is capable of influencing vital cell functions, although they do not exclude the possibility of corrosion products from the magnets contributing to previously observed cytotoxic in vitro and biological in vivo effects.