Abstract: The tidal volume indicator consists of a spirometer in conjunction with a ventilator system adapted for use for small children and neonates. The ventilator system incorporates valving to segregate the component parts into a machine system and a patient system and includes a unidirectional check valve between the exhalation valve manifold and the patient system. The tidal volume indicator includes a spirometer with read-out amplifier operatively connected therewith which enables the volume to be read accurately from between, for example, 0 and 150 ml. It consists of a rack and pinion assembly connected to the vertically moving shaft of the spirometer and a volume indicator needle in conjunction with the necessary scale. Also included is an adjustable warning operating device which will actuate an alarm or indicator if the preset volume deviates by a predetermined amount.