Transtracheal administration of oxygen is a new technique for long term treatment. Twenty patients with hypoxaemia due to chronic obstructive airways disease were studied while receiving oxygen through a microcatheter inserted percutaneously into the trachea. By bypassing most of the dead space and avoiding oxygen wastage at the face this method of delivery reduced oxygen requirements by roughly half compared with delivery through nasal cannulas, thus reducing costs and facilitating portable treatment. Twelve of these patients continued to use the system for up to 13 months in preference to using nasal cannulas. Two important complications were a staphylococcal infection and a fractured catheter. Transtracheal oxygen reduced breathlessness and helped patients with routine daily activities. Transtracheal administration of oxygen is a practical method of treatment which may have an important role in rehabilitating patients with chronic lung disease.