Five patients with radiographic and computed tomography (CT) evidence of extensive pleural thickening were studied. All had a restrictive ventilatory defect. The single breath carbon monoxide transfer factor (TLCO) was reduced in each case (mean 76% predicted) but in four patients the transfer coefficient (KCO) was increased (mean 116% predicted), which is consistent with lung 'en cuirasse'. Static pressure-volume curves of the lungs showed that the maximum transpulmonary pressure was greater than normal and pulmonary compliance was reduced; the curves were therefore indistinguishable from those obtained in patients with pulmonary fibrosis. Transdiaphragmatic pressures during maximal inspiratory efforts were moderately impaired and the proportions of each tidal breath contributed by anterposterior (AP) motion of rib cage and abdomen were similar to normal in both erect and supine postures, suggesting that diaphragmatic mobility was well preserved.