The lungs of 450 coal miners who had been studied previously in a long-term epidemiologic project at 24 British mines have been examined post-mortem for signs of dust-related fibrosis and emphysema. Reliable estimates of cumulative (working-life) exposures to respirable mine dust were available for 342 of the men. The relative frequency of emphysema increased with age at death, and both panacinar and centriacinar emphysema occurred more frequently in smokers than in nonsmokers. The proportion of subjects with any emphysema was 47% in 92 men with no palpable dust lesions, 65% in 183 with small, simple pneumoconiotic lesions, and 83% in 175 miners with massive fibrosis (PMF). The chance of finding centriacinar emphysema in those with PMF increased significantly with increasing exposure to coal dust in life (p less than 0.025). A similar but less convincing relationship was found in those with simple pneumoconiosis (p less than 0.11), but in both groups, increasing amounts of ash with a given exposure to coal reduced the probability of finding centriacinar emphysema. The occurrence of centriacinar emphysema was associated also with increasing amounts of dust retained in the lungs. A preliminary exploration of this association did not support the hypothesis that emphysematous lungs clear dust less efficiently. We conclude that the association observed between exposure to respirable coal dust and emphysema in coal miners indicates a causal relationship. However, because it can be demonstrated only for men whose lungs show some dust-related fibrosis, it is suggested that the extent and nature of such fibrosis may be a crucial factor in determining the presence of centriacinar emphysema.