Long-term asbestos workers who insulate pipes and boilers may develop interstitial lung disease associated with loss of lung function. To quantitate annual loss of lung function, 77 individuals with chest X-rays greater than or equal to 1/0 ILO category who were life-long non-smokers or ex-smokers for greater than 5 years were evaluated. Study parameters included pulmonary function tests and bronchoalveolar lavage for a mean of 3 visits over 30 +/- 2 months. The study participants were 56 +/- 1 years old and had 31 +/- 1 years' occupational exposure to asbestos. At the first visit, multiple regression analysis revealed significant associations between rales or radiographic opacities and VC, FEV1, and total lung capacity; significant associations were also found between neutrophils/ml lavage fluid with FEV1 and diffusing capacity (all p less than 0.05). Annual declines for the asbestos-exposed were VC -92 +/- 28 ml/yr and FEV1 -66 +/- 21 ml/yr. Declines in VC and FEV1 were less in those with reduced lung function at the initial visit. There were no significant associations between any of the annual declines and cells recovered by bronchoalveolar lavage. Compared to other asbestos-exposed cohorts followed longitudinally, asbestos insulators with radiographs greater than or equal to 1/0 and exposure greater than or equal to 20 years have larger rates of FVC and FEV1 decline for both non-smokers and ex-smokers.