Studies on the interaction of magnetic fields and biological organisms1 have centred on the influence of applied magnetic fields on the physiology and behaviour of organisms, including humans, and a search for magnetic sources within the organisms themselves. Evidence continues to accumulate that a wide range of organisms, from bacteria to vertebrates, can detect and orient to ambient magnetic fields (for examples see refs 2–4). Since the discovery that magnetic orientation by bacteria was due to the presence within the organism of magnetic particles of the ferric/ferrous oxide, magnetite5,6, the search has begun for other biogenic deposits of inorganic magnetic material and ways in which the possession of such material might confer on the organism the ability to orient to ambient magnetic fields. Such magnetic material, often identified as magnetite, has been discovered in bees7, homing pigeons8,9, dolphins10 and various other organisms4, including man11. A variety of hypotheses for the use of magnetite in magnetic field detection have been proposed12,13. We report here that bones from the region of the sphenoid/ethmoid sinus complex of humans are magnetic and contain deposits of ferric iron. The possible derivations and functions of these deposits are discussed.