The article deals with the health hazards caused by mineral dusts, and by asbestos fibres in the induction of cancers in particular. Mineral dusts cause damage by inhalation, rarely by ingestion or ingress into the skin. In the lung, bronchitis, fibrosis (pneumoconiosis), and cancers may result. Few mineral dusts cause cancers, and asbestos is unique in causing two separate types within the lung. Epidemiological and other studies of groups of asbestos workers have shown important differences in risk with the type of fibre and the type of job. All types of asbestos cause fibrosis and an excess of bronchial cancers which are, however, also closely cigarette related. Crocidolite is especially related to cancers of the surface of the lung (mesotheliomas). Mining and milling of chrysotile, the most used type of asbestos, have caused few mesotheliomas, despite heavy dust exposures in the past. The diseases induced by asbestos are dose-related. Where it has been possible to divide the groups of asbestos workers into those with different levels of past exposure, the least exposed groups have shown small or no excess of asbestos-related diseases despite their exposures having been considerably higher than that likely to have been encountered by the general public. Present evidence indicates that the general public have not been at risk of asbestos-related diseases, but more evidence is required about the proportion of all mesotheliomas which are related to asbestos. The new techniques of mineralogy when applied at a micro level to the dust in tissues, and particularly in the lung, may be of great help in answering this important problem. Some comparisons of the mortality from occupationally related cancers, accidents, smoking habits, and general diseases are given. Current research into the biomedical effects of natural fibrous mineral dusts is likely to be of great value in ensuring that the new man made mineral fibres now being developed are manufactured and used under circumstances which will cause no ill effects to health.