To clarify the clinical value of the International Labor Office (ILO) roentgenographic classification of pneumoconiosis in assessing asbestos-exposed persons, we determined the relationships among spirometric values, radiographic evidence of parenchymal pulmonary fibrosis and/or pleural thickening, and cigarette smoking history in 684 consecutively enrolled male plumbers and pipefitters participating in a larger cross-sectional prevalence study. The subjects were mainly marine pipefitters (35%), plumbers (24%), and steamfitters/welders (23%); 28% had never smoked, 39% were ex-smokers, and 33% currently smoked cigarettes. Mean values for FVC and FEV1 were 95.0 and 91.9% of predicted, respectively, with mean FEV1/FVC ratio 77.7%; by standard criteria, 7.8% had restrictive impairment, and 21.7%, obstructive defects. Chest radiographs were normal in 63% and showed pleural abnormalities only in 17%, parenchymal abnormalities only in 7%, and both pleural and parenchymal abnormalities in 12%. Both FVC and FEV1 correlated with the degree of small opacity profusion, as assessed by ILO grade. Pleural abnormalities were associated with lower FVC values, independently of ILO profusion grade for Grades less than or equal to 1/0, and were unexplained by smoking status. In addition, there was a positive association between smoking history and degree of ILO parenchymal abnormality, particularly in those with the heaviest cumulative smoking history. Our results suggest that the ILO classification of pneumoconiosis, although a useful epidemiologic tool, should be applied with caution in persons with asbestos exposure, and that pleural abnormalities may be associated with physiologic impairment in such persons.