Sixty-six cases of mica pneumoconiosis have been reported in the literature. Twenty-six of the cases suggest that pneumoconiosis may be caused by pure mica alone. In only six cases the diagnosis was based on clinical examination, radiography, and lung biopsy or autopsy results. In one of these six, doubt was raised by the authors about the purity of the mica exposure. Seven epidemiologic studies have been performed among mica-processing workers, and these studies are all cross-sectional. In addition 30 experimental investigations have been carried out. However, there are no controlled inhalation studies among them. The results from the intratracheal instillation studies do not give a unanimous conclusion as to whether pure mica is fibrogenic or not. Present knowledge suggests that pure mica is moderately toxic and may induce pneumoconiosis. Exposure to mica is usually associated with exposure to other minerals such as quartz and feldspar.