ObjectiveTo assess the effect of topical betahistine on Eustachian tube function in subjectively abnormal subjects in a hyperbaric chamber.MethodActive and passive Eustachian tube function was examined using tympanometry in a pressure chamber.ResultsActive Eustachian tube function was tested against the negative middle ear pressure induced by increasing the chamber pressure to +3 kPa. One voluntary swallow decreased middle-ear pressure by a mean of 1.36 kPa. Passive Eustachian tube function was tested by measuring spontaneous Eustachian tube openings as the chamber pressure dropped from +10 kPa to ambient. Four distinct patterns of Eustachian tube behaviour were seen, three of which indicated Eustachian tube dysfunction. Betahistine had no positive effect on Eustachian tube opening, although previous animal studies had suggested a beneficial effect.ConclusionTopical betahistine had no effect on Eustachian tube function. Combining a hyperbaric chamber with tympanometry proved ideal for evaluating Eustachian tube function.