With the general improvement in environmental controls in workplaces where asbestos is used, an increasing number of workers are seen who exhibit isolated pleural plaques. The question as to whether these are associated with respiratory impairment independently of parenchymal disease remains unresolved. The question was reinvestigated using quantitative gallium-67 lung scanning to take into account early parenchymal change not evident on the chest radiograph. We carried out a cross-sectional study of 110 construction insulators all currently at work. Overall, 58.2% had pleural abnormality, 52.5% pleural plaques only, and 5.5% diffuse pleural thickening as assessed from the PA chest radiograph. Compared with those without, those with any pleural abnormality had a decrease in FEV1 and FVC on average of 222 and 402 ml (p less than 0.05), and those with isolated pleural plaques, a decrease on average of 200 and 350 ml (p less than 0.05), after taking into account age, height, smoking status, and the presence of parenchymal abnormality as assessed by chest radiography and gallium uptake. The complaint of dyspnea with strenuous activities was also significantly related to the width and extent of chest wall pleural thickening (p less than 0.05), independently of parenchymal disease. This study suggests that the most common radiographic findings in asbestos-exposed, isolated pleural plaques are associated with a significant reduction in FEV1 and FVC, which cannot be attributed to the presence of radiographic and subradiographic pulmonary fibrosis.