In many cases speech and pure tone audiometry are not practicable. Therefore, the hearing aid fitting is based on objective techniques, like the measurement of the stapedius-reflex threshold or acoustically evoked neural responses. In particular, brain stem responses are very helpful for an objective hearing-aid fitting. They represent the full scale of hearing dynamics and supply direct information for selection and adjustment of the hearing aid. Control of the fitting can also be effected directly by measuring brain stem responses.