I used ventilatory muscle training by means of repeated runs of isocapnic hyperpnea to improve ventilatory muscle function in two patients with acute respiratory failure superimposed on chronic obstructive lung disease (COPD). The training was associated with successful weaning from mechanical ventilation and a rapid return to adequate ventilatory function. This method is easy to use and can be started while patients are still intubated. Furthermore, continued post extubation ventilatory muscle training provides further improvement in ventilatory muscle function.