The Vienna Group uses two types of cochlear prosthesis, a unichannel extracochlear and a four-channel endocochlear device with unichannel stimulation. The limitations in patient selection are the same for both, except for the auditory status. My answer to the first two questions therefore involves a definition of what we call deafness and residual hearing. The endocochlear four-channel prosthesis is limited to patients who have bilateral deafness with pure-tone thresholds above 95 dB, with or without hearing of words, absence of noise discrimination, and no visual unaided word or sentence comprehension even with the use of bilateral hearing aids. The extracochlear unichannel prosthesis is limited to patients who have pure-tone thresholds of 85 dB and above, hearing of words but no visual unaided word or sentence comprehension even with the use of hearing aids. The main difference here is that the patients of this group are able to understand some numbers and to discriminate environmental sounds. This very important function must be preserved. This is only possible with an extracochlear device. Regarding the question of pre- or post-lingual deafness, I should like to state that the majority of our 35 patients were post-lingually deaf. Only recently we accepted a small number of pre-lingual deaf patients, though one should realize that the rehabilitation of speech comprehension in these patients takes much longer than in the post-lingual deaf and that the results achieved after a reasonable rehabilitation period can only be compared within the same group of pre-lingual deaf patients, because it will probably never be as good as in the post-lingual deaf group. To questions number 4 and 5, concerning age limitation, I should like to comment that it seems very reasonable to me to decrease the age below 13-15 years which is now our present age limitation. There are nevertheless also a few valid arguments against this. In most patients below 10 years it is very difficult to obtain reliable data with preoperative electrical stimulation-a subjective test which has to be performed under local anaesthesia. The second argument concerns the post-operative rehabilitation. From my experience it seems to be very difficult to effect a consistent rehabilitation procedure because of various psychological and environmental circumstances. These objections are probably not justified with the age group of 24 years because their rehabilitation coincides with the physiological development of speech and hearing. I believe that this age group should be our future goal when it becomes possible to test the electrical sensitivity of nerve fibres objectively, for example, with the registration of electrical evoked BSP under general anaesthesia; only extracochlear stimulation would be warranted in small children. Besides the audiometric criteria mentioned, we have the following restrictions to cochlear implants.