Five hundred and fifteen men newly attending chest clinics in coalmining areas of England and Wales were entered into a study of the risk of irregular opacities on the chest radiograph in relation to occupation; readable radiographs were received for 489. The men completed questionnaires on occupational and smoking history and the radiographs were read for irregular opacities by the collaborating chest physicians and by a panel of three readers using the ILO 1980 classification. Older men had more irregular opacities than younger men, but coalworkers had a significant excess risk of nearly three times of having irregular opacities, which remained after stratifying for smoking and age. Lung cancer was evident on 14% of the radiographs and was significantly less common in coalworkers than non-coalworkers. The findings are consistent with a causal association between coalwork exposure and irregular opacities. Other evidence suggests that these opacities are associated with emphysema in coalworkers.