<prompt> The most commonest site of bleeding in haemoptysis isTracheobronchial treePulmonary parenchymaPleural diseaseAll the above  <response>: Ref Harrison 19 th edpg 1793 The most common source of bleeding in massive hemopthaemo are the bronchial aeries which are pa of the high pressure systemic circulation . In bronchitis, bronchiectasis or with endobronchial tumors. Ref Harrison 19th edition pg 1793 