It is due to the escape of chyle from the thoracic duct in the pleural cavity. It may be due to the rapture of thoracic duct due to the surgery or malignancy or congenital anamolies. The clinical manifestations are similar to the pleural effusion or pyothorax. The diagnosis is established when thoracentesis reveals a milky white fluid. The biochemical analysis shows high triglyceride level. The bed side test for chyle may be done by shaking the chyle with alkali or ether. If it is a chyle it becomes clear.