The thickness of morphoea plaques was measured by A-mode ultrasound and compared to regional control measurements in the same individuals. The thickness of morphoea plaques was increased by 18-310% in 17 patients with one or a few morphoea plaques (p less than 0.01), and by 13-145% in 6 patients with generalized morphoea (p less than 0.05). The increase in thickness of morphoea plaques was local confined to the plaques. Ipsilateral and contralateral control measurements were not different, and measurements in a standard region (forearm) were not different from those in a group of healthy controls matched for sex and age. Plaques of clinically 'advanced' scleroderma were more thickened (p less than 0.01) than plaques of 'slight' scleroderma. The relative increase in thickness was larger (p less than 0.01) in skin with a habitual thickness of 0.8-1.1 mm. The habitual skin thickness on the extremities (mean 1.0 mm) was less (p less than 0.01) than on the trunk (mean 1.5 mm), and, consistently, plaques with 'advanced' scleroderma were more frequent (p less than 0.05) on the extremities. Ultrasound measurement of skin thickness was accurate with SD form 0.05-0.09 mm and coefficients of variation from 3-7% in reproducibility studies of typical morphoea plaques as well as normal appearing skin.