The development of Otitis media has been related to abnormal Eustachian tube (ET) mechanics. The ET is a collapsible tube that is periodically opened to regulate middle ear (ME) pressure and clear ME fluid into the nasopharynx. The ability to perform these physiological functions depends on several mechanical properties including the ET's opening pressure (P_open), compliance (ETC), and hysteresis (). In this study, a previously developed modified force-response protocol was used to determine ET mechanical properties after experimental manipulation of the mucosal surface condition. Specifically, these properties were measured in the right ear of 6 cynomologous monkeys under baseline conditions, after "washing out" the normal ET mucous layer, and after instillation of a pulmonary surfactant, Infasurf. Removal of the normal mucosa did not significantly alter P_open, but did result in a decrease in ETC and (ANOVA, p<0.05). Treatment of the mucosa with Infasurf was effective in reducing P_open and increasing both ETC and to baseline values (p<0.05). These results indicate that the mucosa-air surface tension can affect the overall compliance and hysteretic properties of the ET. In addition, this study indicates that surfactant therapy may only be beneficial in patients with rigid or inelastic ETs (large P_open and low ETC and ).