Although restriction is considered the classic pulmonary function profile of asbestosis, studies suggest that obstruction of the peripheral airways not revealed by standard spirometry is equally frequent and indicative of peribronchiolar fibrosis. We recorded flows and volumes from maximal expiratory flow volume (MEFV) curves, closing volume data and the phase III slope of the alveolar plateau for 610 litigants, 575 men and 35 women, exposed to asbestos for varying periods in a single workplace in northern New Jersey. Smokers (260) included current smokers and subjects who had stopped within the previous 10 years; nonsmokers (350) had either never smoked or had given up for more than 10 years. Analyses were made for both groups according to years worked. Compared to predicted, smokers and nonsmokers had significantly higher closing capacities (p less than 0.01) and delta N2% (p less than 0.001) means, and lower forced vital capacity (FVC), forced expiratory volume for the first second (FEV1.0, maximal expiratory flow rate (MEFR) and peak expiratory flow rate (PEFR) functions (p less than 0.05); the flow rate after 75% of the FVC had been exhaled (FEF75%) values were significantly reduced (p less than 0.01) only for workers exposed for more than 30 years. The change from predicted was significantly more rapid for smokers, compared with nonsmokers, for FVC, FEV1.0, PEFR, MEFR and FEF75% means, while the increase in closing capacity (CC) was twice as rapid for nonsmokers and the two groups did not differ in their mean rates of rise for delta N2%. CC and the slope of the alveolar plateau appeared to be the measures best able to discriminate between the data for both smoking and nonsmoking asbestos workers and their lung function prediction means.(ABSTRACT TRUNCATED AT 250 WORDS)