Eustachian tube function was evaluated in 27 children (32 ears) with tympanostomy tubes at 6-week intervals for 12 to 30 months. Using a modified inflation-deflation test of passive and active ventilatory function, it was found that the ears had persistent functional obstruction. Most ears exhibited no significant change in tubal function throughout the observation period. There was no difference in the ventilatory function when the nasal airway was congested (other than due to purulent upper respiratory tract infection) and not congested. However, significant seasonal effects on Eustachian tube ventilatory function were recorded: function was poorer in the winter than in the summer. No relationship was found between Eustachian tube ventilatory function and the age of the child.