Abstract: A maximum expiratory vital capacity maneuver is produced in an infant by a method which comprises the steps of1) inflating the lungs of an infant with air synchronously with natural tidal inspiration to a lung volume greater than that reached at end-tidal inspiration for a number of respiratory cycles until the infant's natural tidal breathing pauses;2) during the pause in breathing, rapidly inflating the infant's lungs to substantially total lung volume;3) immediately compressing the chest and abdomen of said infant to produce a maximum forced expiration.The data generated by measuring flow rates and volumes during this maneuver can be used to derive the conventional measurements of pulmonary function for such infants and provide an opportunity to compare those measurements with the corresponding measurements obtained for adults and older children who are capable of performing the maneuver voluntarily under instructions.