SummaryThe effects on pulmonary function of removal of bullae occupying at least 30 per cent of a hemithorax are reported in 15 patients, 10 of whom had associated chronic obstructive lung disease. All patients with dyspnea improved symptomatically after surgery. Lung function, measured six to twelve months after surgery, was significantly improved: mean (±I SD) FEV, preoperative was 48±26% predicted and postoperative 70±26 % predicted (p<0.001); Pa02preoperative 66±9 mm Hg vs. postoperative 78±10 mm Hg (p<0.05). The largest increase of FEV, was obtained in patients with giant bullae and only slight generalised emphysema. In the seven patients with a follow-up of two to five years after surgery, the mean postoperative annual decline in FEV, was 49±51 ml.