This prospective study was designed to determine the efficacy of iodized talc pleurodesis in patients with pleural effusions. Thirty-four patients underwent this treatment (three bilaterally) between October 1, 1989, and March 31, 1991. All patients had to have complete or nearly complete lung reexpansion after tube thoracostomy with fluid drainage less than 100 ml in 24 hours. A slurry containing 5 gm of talc and 3 gm of thymol iodide was instilled into the pleural space through the chest tube. Chest tubes were removed after complete reexpansion and clearing of the effusions, usually in 3 to 5 days. The patients' ages ranged from 26 to 88 years (average 50 years). Eighteen patients had lung carcinoma, two had mesothelioma, and one each had carcinoma of the ovary, breast, or anorectum, multiple myeloma, schwannoma, or Hodgkin's lymphoma. Two patients had an unknown adenocarcinoma primary and five other patients had acquired immunodeficiency syndrome. One patient had congestive heart failure. Nineteen patients had left, 12 had right, and three had bilateral pleural effusions. The effusion was serosanguineous in 26 and serofibrinous in eight patients. Serial chest radiography showed complete response in all patients. The period of follow-up ranged from 1 to 21 (average 4.9) months, with no recurrences. Twenty-three patients have died during the follow-up period, and there was no sign that reaccumulated pleural effusion existed in any, despite clinical evidence of systemic tumor progression. These observations indicate that intrapleural instillation of a slurry of iodized talc is a safe, adequate, and effective treatment for control of neoplastic or benign pleural effusions.