Seventeen ears of 12 subjects with normal hearing were tested in both a laboratory and a clinical setting to study impedance changes in normal human ears associated with the acoustic reflex. Compliance and resistance at the eardrum were measured with middle ear muscles relaxed and contracted by means of a contralateral noise stimulus, respectively. The reflex induced impedance changes were compared to similar impedance data obtained by other investigators, and to typical otosclerotic impedance values. The reflex is shown to affect the impedance by a decrease in compliance and a slight decrease in resistance.