This article provides a selective review on the perspectives of the clinical research and application of the mismatch negativity (MMN), a component of the auditory event-related potential generated by the brain's automatic response to any discriminable change in auditory stimulation. The MMN (and its magnetic equivalent MMNm) currently provide the only objective measure of auditory discrimination and sensory memory. It can be registered in the absence of attention and with no task requirements, which makes it particularly suitable for studying different clinical populations and infants.