This study has been undertaken to help determine how the perception of phonemes is important in the development of language and speech in deaf children. It is generally accepted that a pure tone audiogram is not a reliable indication of future language development, and consequently it is necessary to look for other prognostic tests. The development of these tests would be of great value not only in the prognosis but also in helping to reveal the basic underlying mechanisms in speech perception and production. This could in turn lead to a more definitive approach to the aural rehabilitation of the patient.