Two cases of adult respiratory distress syndrome due to diffuse pulmonary haemorrhage are reported. The first patient was treated with azathioprine, prednisolone, cyclosporine and ranitidine for haemorrhagic rectocolitis; the second has untreated primary biliary cirrhosis. Haemoptysis only occurred in the latter. Both had severe isolated hypoxaemia. Chest X-rays revealed bilateral alveolar infiltrates. Bronchoscopies showed a diffusely bleeding bronchial tree. Both patients recovered after having been mechanically ventilated with positive end-expiratory pressure for six and eight days respectively. The cause of the diffuse pulmonary haemorrhage was, in the first case, severe thrombocytopaenia (17,000 G.1-1) of central origin, and, in the other patient, an unspecified vasculitis. Diffuse pulmonary haemorrhage should be added to the list of possible causes of the adult respiratory distress syndrome.