Intermittent mechanical ventilation is a frequent form of therapy for respiratory failure in children. Due to its difficult application in patients with high respiratory rate and difficult synchronization with the respirator, intermittent mandatory ventilation (I.M.V.) was tried on these patients, introducing a unidirectional valve, connected to a continuous flow of gases, on the inspiratory side of the respirator. With I.M.V. the patient is able to breath spontaneously the gases coming from the unidirectional valve and at the same time the respirator provides periodical insuflations at a frequency previously determined by us. The pressure generated by the respirator in the respiratory circuit, closes the unidirectional valve sending gases to patient. This technique not only reduced time of application of mechanical ventilation but made weaning shorter, easier and safer.