A system for determining the hearing ability of an individual comprises a generator for generating a test stimulus signal, a hearing aid (2) having a digital signal processor for processing said test stimulus signal and converting it in order to output an acoustic stimulus signal, and a first synchronizing means. The system further comprises an electrophysiological instrument (1) having a second synchronizing means, and means (7) for establishing from said individual an evoked response to said acoustic signal. The first synchronizing means and said second synchronizing means exchange a synchronization signal in order to synchronize said evoked response to said acoustic stimulus signal. The invention also provides a hearing aid and a method for carrying out electrophysiological measurement of the hearing ability of an individual.