This paper reviews recent applications of mechanical ventilation such as controlled hypo ventilation in acute asthma, domiciliary nocturnal ventilation in chronic respiratory failure due to neuromuscular disease and improvement of left ventricular performance by raised intrathoracic pressure. Established uses of mechanical ventilation include control of respiratory failure, intracranial pressure and pulmonary hypertension while other uses such as internal splinting of flail chest, simultaneous ventilation-compression cardiopulmonary resuscitation and prophylactic postoperative ventilation are more controversial.