The clinical electrocochleography essentially allows the registration of the global action potential of the acoustic nerve. The use of acoustic stimulations with alternating polarity eliminates the cochlear microphonics. In severe deafness, where no action potential can be registered, even not with maximal acoustic impulses, it can be interesting to register the microphonic potentials. This can be done by using acoustic stimulations with the same polarity. If some microphonic potentials can be registered by this technique, one can assume that the ciliated cells are -- at least partially -- unaffected and that the cause of the deafmess in neurogenic. This test thus allows a primary differentiation between sensory and neural deafness. Some clinical cases illustrate this phenomenon.