It is well known that sensory deprivations could cause plastic changes in neural populations involved in sensory processing [1-7]. Positron emission tomography (PET) has recently been used for physiological and biochemical measurements in different brain areas [8, 9]. Using PET, Wanet-Defalque [8] has demonstrated a higher glucose metabolism rate in the occipital cortex in human subjects who became blind early in life. It seems interesting to know whether the same high brain activity exists in the auditory cortex of deaf patients. We would like to present the metabolic activity in the brain, as measured by PET, in human subjects with either early or adult loss of hearing compared to controls with normal hearing.