An investigation was conducted to measure the degree of airway obstruction in asbestos (1332214) exposed workers in ship construction and repair and to relate the results to the signs of asbestosis on chest radiographs. Measurements of pulmonary function were made on 296 male boilermakers who had been exposed to asbestos for more than 15 years. While most had been involved in ship repair, some had built new ships as well. Pulmonary parenchymal asbestosis was correlated with worsening airway obstruction. Increasing profusions of irregular opacities of asbestosis were associated with more obstruction. These results established an observational continuum between observations of airway obstruction, especially of small airways in insulators who were heavily exposed to asbestosis but had not yet demonstrated asbestosis on chest radiographs, and advanced asbestosis. The authors conclude that it appears that as increasing numbers of small airways are permanently obstructed, forced vital capacity progressively decreases. As the process continues to worsen, so many small airways are obstructed that the slowly ventilated space is lost and vital capacity is small but quickly emptied so forced expiratory ventilation at 1 second is restored together with flows. Diffusing capacity is closely tied to alveolar volume and remains so until it is critically reduced. The greater impairment in shipyard workers reflects the hours of work in a container of limited volume into which are generated effluents of welding, insulating, metal grinding and polishing, painting, and other surface coating.