Changes in ventilatory function measurements of United States miners who had participated in two surveys held nine years apart were analysed in relation to smoking habits, dust exposure, and other factors. The results showed trends similar to those reported among British miners. Loss of FEV1 over time and found to be related to smoking (0.1 litre excess decline in current smokers compared with those who had never smoked over 11 years) and to occupational exposure (0.036-0.084 litres over 11 years, depending on the index used). The results offer confirmation of the relationship between work in coal mines and loss in ventilatory function observed in British miners, and also seen in cross sectional studies.