The middle ear inertial component of bone-conduction hearing was studied in 8 normal-hearing young adults. The inertial component was eliminated to varying degrees by introducing various positive and negative air pressures into the ear canal. Sweep-frequency Békésy tracings were obtained from 100 through 5 000 Hz for bone-conducted pure tone stimuli while the air pressure of the test ear was varied and the nontest ear was masked. Air pressures of +/- 100, +/- 300, and +/- 500 mm H2O were utilized. Results revealed maximal shift in the mid frequencies (750 Hz) and an increase in effect with increase in pressure. A second prominent region of threshold shift emerged at 2 000 Hz for the +/- 500 mm H2O air pressure conditions. Considerable variability in the magnitude of threshold shift and in the frequency region of maximum shift was observed.