The problem of determining the cochlear reserve of the otosclerotic patient is of critical importance to the otologic surgeon. There are two reasons for this fact. In the first place, it is impossible to predict accurately the postsurgical level of a patient's hearing unless a reasonable estimate of cochlear reserve can be made preoperatively. The surgeon cannot calculate the outcome anticipated for his patient unless he knows the patient's sensorineural acuity. Only if he has this information at hand is he in a position to take into account figures such as Dr. Lawrence has been giving us regarding the acoustic contribution of the conductive mechanism. Secondly, there is the equally important task of evaluating different surgical procedures. The determination of the relative success of each new procedure can be more precise if one can state how nearly it restores patients to the level of their sensorineural capacity. The surgeon can