Pleural sclerosis after drainage with a small-bore catheter was performed in 21 patients with malignant pleural effusions. Intrapleural catheters 7- to 24-French in size were placed by using sonographic guidance. Tetracycline (18 patients) and bleomycin (four patients) were used as sclerosing agents (one patient had both). Clinical and radiologic follow-up was available on all patients until they died (range, 2 weeks to 25 months; mean, 3.6 months). Pleural sclerosis was successful in 15 (71%) of 21 patients. Two patients in whom pleurodesis failed had pleural sclerosis repeated, with one success and one failure. All of the failures were in patients in whom the amount of chest-tube drainage was more than 100 ml/day. Pleurodesis with tetracycline was painful in six patients; no pain was associated with use of bleomycin. Small pneumothoraces developed in four patients at the time of chest-tube placement, without consequence. A superimposed infection that developed in a patient having continuous drainage of pleural fluid was successfully treated with antibiotics. Pleural sclerotherapy can be performed through sonographically placed small-bore catheters with results comparable to those seen with large-bore, surgically placed catheters.