Closing volume and closing capacity were determined in 82 working Appalachian coal miners and in a comparable group of control subjects. Abnormalities of closing volume and closing capacity were related to other measurements of pulmonary function. The relationship of smoking history, dust exposure, and presence of pneumoconiosis and bronchitis to elevations of closing volume and closing capacity was determined. It was shown that nonsmoking miners had elevated closing volume and closing capacity when compared to control subjects. Miners who were smokers or ex-smokers also had elevated closing capacity when compared to control subjects. Neither bronchitic symptoms nor the radiographic presence of pneumoconiosis were associated with an elevation of closing volume or closing capacity.