OUTLINE: This is a randomized study. Patients are stratified according to participating institution. Patients are randomized to one of two treatment arms. Arm I: Patients undergo pleurodesis. A chest tube is inserted, the pleural fluid is drained for 24 hours, and the lung is re-expanded to at least 90% of full expansion. Within 24-36 hours patients undergo sclerosis with talc slurry injected into the chest tube, which is then clamped. Patients are rotated in all possible directions, holding each position for about 30 minutes. After 2 hours the chest tube is unclamped and reattached to suction drainage, which is strictly measured for 24-hour totals. Following a decrease in drainage to no more than 150 ml/24 hours (usually by the second or third day postsclerosis), the chest tube is removed. Arm II: Patients receive thoracoscopic insufflation. The chest is explored thoracoscopically via single or multiple incisions using direct or videothoracoscopic visualization, and the lung is re-expanded to 90% of full expansion. Dry talc is pneumatically insufflated into the chest, with complete dispersion throughout the hemithorax. Following insufflation, the chest is drained via a chest tube, which is removed when the drainage is no more than 150 ml/24 hours (usually by day 2 or 3 following insufflation). Patients are removed from study for disease progression or an unsuccessful lung re-expansion. Patients are followed monthly for 6 months for relapse and survival.