Pleural lesions in crocidolite workers from Western Australia.

Exposure to asbestos can cause benign pleural lesions, the most common of which are parietal plaques. Diffuse fibrotic changes of the pleura can also occur.' The clinical significance of plaques is slight. Diffuse pleural thickening, on the other hand, can lead to a considerable decrease in lung function.`3 The International Labour Office (ILO) system for classification of pneumoconioses does not differentiate large pleural plaques from diffuse pleural thickening.4 In populations with a high risk of mesothelioma the occurrence of diffuse thickening relative to plaques is high whereas in pqpulations with low risk of this tumour the opposite is true. 6 It was decided to extend these studies further by investigating patients who had been occupationally exposed to crocidolite (blue asbestos) and had a known high risk of mesothelioma.7