Tympanometry was performed under the contraction of the middle ear muscles (dynamic tympanometry). A tympanograrn of lesser compliance was observed under a stapedius reflex which was produced by contralateral acoustic stimulation. In patients with reversed (downward) stapedius reflex, the dynamic tympanogram showed either a higher peak amplitude or a shift of conventional tympanogram to the negative pressure side. Voluntary contraction of the tensor tympani produced a lesser compliance with positive pressure, whereas there was an apparent increase of compliance with negative pressure in the external auditory meatus. A shift of the dynamic tympanogram to the negative pressure side was interpreted as being due to contraction of the tensor tympani muscle. Dynamic tympanometry may also be utilized as a recording of reflex decay.