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Effusions associated with malignant mesothelioma are strongly exudative, with elevated total protein concentrations in the range of 4 to 5 g/dL. Pleural fluid lactate dehydrogenase concentrationoften exceeds those of patients with carcinomatous pleural effusions, with levels greater than 600 IU/L. However appoxiametly 5% of malignant pleural effusions can be transudates. This article describes a case of malignant pleural mesothelioma causing transudate. A 74 year-old male patient who was admitted to the clinic had a one-year history of pleuretic chest pain and exertional dyspnea. In the biochemical analysis of pleural fluid, glucose concentration was 120 mg/dL, LDH was 11 U/L, and total protein was 0.5 g/dL.Repeated biochemical analyses were consistent with transudate. The diagnosis was proved by open pleura biopsy in this patient. Malignant transudative effusions are often due either to concomitant congestive heart failure, atelectasis from bronchial obstruction or pulmonary embolism. However, no coincidental disease was found. The probable cause was trapped lung and early stages of lymphatic obstruction. To date, this is our only patient with malignant mesothelioma causing transudate.