Employing inflation-deflation and forced-response tests, the eustachian tube (ET) function was evaluated in six adult human subjects with traumatic perforation of the tympanic membrane and otherwise negative otologic histories; and 15 juvenile or adult rhesus monkeys with freshly created myringotomy perforations of the tympanic membrane and otherwise documented normal middle ears. The study findings demonstrated that the rhesus monkey ET functions as a scaled down model of the ET of man, exhibiting a shorter tubal dilation duration and a lesser capacity to pass air. When ET function in the two species was compared using a dimensionless measure expressing the tubal dilation efficiency, the operational biomechanics of both systems were found to be almost identical. These observed functional homologies between man and the rhesus monkey ET systems suggest that the rhesus monkey is a suitable animal model in which to study the pathogenesis of otitis media with effusion, stemming from ET dysfunction.