Fibrous clays, such as attapulgite and sepiolite, are used in a variety of applications which may lead to inhalation exposure. Aerosols of these materials were produced experimentally and airborne particles examined with the transmission electron microscope. Although the particles appeared to be compact conglomerates of non-fibrous material, many discrete fibres were found in the lungs of rats which had been exposed to them. This indicates that the particles contain a fibrous component which is releasedin vivo. This effect was reproduced by treating aqueous suspensions of particles by either hand shaking or sonication. It would appear that microscopical examination of an airborne dust alone may fail to provide an indication of a potential‘fibre hazard
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