Radiological and clinical findings in workers certified and not certified as having asbestosis by the Medical Panel of the British Pneumoconiosis Compensation Board were correlated with pulmonary function tests (PFTs). A total of 19 certified asbestosis cases (15 males, four females; mean age, 52 years; mean exposure duration, 13.5 years), and nine asbestos (1332214) workers, not certified for asbestosis, (all male; mean age, 51 years; mean exposure, 14.2 years) were tested. All subjects were clinically and radiologically assessed without knowledge of the PFT results. Specific PFTs performed included lung volumes, forced expiratory volume at 1 second (FEV1), peak expiratory flow (PEF), dynamic lung compliance, diffusing capacity, arterial oxygen saturation, and airway conductance and gas volume. The highest discriminant power was found in inspiratory, vital, and diffusing capacities; inspiratory or vital capacity alone exhibited such powerful discrimination that no other tests added significant improvement. Means of the PFT parameters were not significantly different between the certified and uncertified groups. Seven of 24 workers tested for oxygen saturation were abnormal, and poorly correlated with subjective breathlessness and diffusing capacity. Mean FEV1 in the certified workers was 52 percent of the uncertified group, but the FEV to VC ratio was similar in both groups, indicating that the ventilatory defect indicated by FEV1 was due to restriction rather than obstruction. PEF was not significantly different between the two groups. The authors conclude that inspiratory, vital, and diffusing capacities demonstrate the best discrimination between the two groups of asbestos workers, and support the Compensation Board's findings.