Chemical sclerosis of the pleural space is used to prevent recurrence of spontaneous pneumothorax. To test whether sclerosis restricts diaphragmatic excursion, we measured diaphragmatic excursion by ultrasonography in subjects with unilateral pleural sclerosis and compared it with diaphragmatic excursions in normal subjects, in subjects with cystic fibrosis (a diffuse bilateral lung disease), and in those who underwent surgical procedures that obliterate the pleural space. In five subjects with unilateral chemical sclerosis, diaphragmatic excursion was significantly less on the sclerosed side than on the contralateral side (10.7 +/- 1.3 vs 17.3 +/- 1.7 mm, mean +/- SEM; p less than .01). Compared with those of normal subjects, the side-to-side differences in excursion were increased by pulmonary disease (p less than .03) and additionally by unilateral sclerosis (p less than .015). There was no significant difference between diaphragmatic excursions on left and right sides of subjects without history of pleural disease. These data suggest that chemical pleural sclerosis causes a measurable reduction in diaphragmatic excursion on the affected side. The physiologic significance of this effect is not known.