A 64-year-old woman was admitted to our hospital with a hemothorax after one year of therapy for angiosarcoma that had arisen from the skin of the head. The hemothorax was believed to have resulted from metastasis of the angiosarcoma. Interleukin-2 (IL-2) at a dose of 20 x 10(4) U once daily was administered intrapleurally. Clinical improvement was first observed on the second day after the first dose of IL-2. Increases in natural and in lymphokine-activated killer activity of lymphocytes in pleural effusion were found on the eighth day. Starting on the 16th day of IL-2 therapy, no more fluid was drained, so administration of IL-2 was stopped. The clinical course indicated that the pleural effusion disappeared not because of pleurodesis but because of the anti-cancer effects of IL-2. There were no marked side effects, and intrapleural administration of IL-2 may be useful in patients with hemothorax due to metastasis of angiosarcoma.