The impedance of the human mastoid was detd. by means of a vibrating piston, 1 end of which was placed in firm contact with the body surface. The impedances of several subjects were measured. The compliance (c) and the resistance (r) were calculated from the results; the avg. values were c = 1.5 X 10-8 cm./dyne and r = 1.0 X 104 dyne/cm./sec., for an area of the piston base of 1 sq. cm. and an application force of 250 g. The impedance depends on the area and the application force of the piston.