We compared computed tomography (CT) scanning with chest radiography in the assessment of asbestos-induced pleural disease (AIPD) in 20 patients (17 men and 3 women, mean age 55 years, range 43-74 years). Involved pleura was scored on plain chest radiographs according to the International Labour Office (ILO) method of evaluating AIPD. A CT score was calculated from the measurement, using a digital length probe, of the circumference of the chest wall involved by pleural disease in each slice. The maximum width of pleural disease was taken into account in a way analogous to the ILO method for the chest radiograph. The CT score correlated with the chest radiograph score (r = +0.82, P less than 0.0006). CT demonstrated discrete plaques in 95% of patients but these were identified only in 59% patients on the radiograph. Diffuse pleural thickening was evident on the CT scan in all patients and in 70% on the radiograph. There was more inter-reader agreement about the type of pleural disease on the CT scans than on the chest radiographs. CT and chest radiograph scores inversely correlated with all lung function measurements except KCO. We conclude that increasingly extensive pleural disease is associated with increasingly severe impairment of lung function. CT scanning demonstrates the type of AIPD better than plain chest radiography.