Effusion recurrence is a major problem in the palliative care of patients with disseminated cancer. Thirty-two patients with recurrent malignant pleural effusions were treated with intracavitary natural beta-interferon at increasing doses (5-20 million units) for a maximum of three administrations. Among 29 evaluable patients, 11 showed complete (27.6%) or partial (10.3%) remission. No difference in response rate was observed according to sex, age, and histological type. All the responses were observed in patients with an effusion volume less than 1,000 ml (11/16; 68.8%). No side effect was observed. In conclusion, intrapleural beta-interferon is promising as a palliative in the treatment of recurrent malignant effusions.