Endostatin is an angiogenesis inhibitor that is an endogenously produced proteolytic fragment of type XVIII collagen. Although serum levels of endostatin have extensively been studied in patients with malignant diseases, endostatin in pleural effusion has not been fully evaluated. In order to determine whether endostatin is present in pleural effusion, and to determine whether endostatin levels vary in pleural effusion of different etiology, we measured levels of endostatin in 38 malignant pleural effusion due to lung cancer patients and 29 patients with non-malignant disease using an ELISA kit. Free form of endostaitn was measurable (>11.2 pg/ml) in 26 of 38 malignant and 13 of 29 non-malignant pleural effusion. Endostatin levels in the 38 malignant pleural effusion were significantly higher than those in patients with the 29 patients with non-malignant diseases (p = 0.0131). However, there was not statistically significant difference between the patients with pleuropneumonia and those with tuberculous pleurisy (p = 0.2194). In malignant pleural effusion due to lung cancer, the pleural effusion endostatin levels did not differ when the histological types of lung cancer were considered(p = 0.0674). Endostatin was present in both malignant and non-malignant pleural effusion, and elevated levels of endostatin were observed in malignant pleural effusion. Although the mechanisms are unclear, elevated levels of endostatin in pleural effusion may represent the local productions of endostatin in pleural space.