We present normative data on the auditory brainstem response (ABR) derived from 91 premature infants, and illustrate a simple procedure that uses deviations from these norms to differentiate a hearing disorder from a neurological disorder involving the brainstem. In an infant intensive care unit the procedure identified 11 patients with hearing disorder, 3 with neurological problems, and 3 with both disorders. Serial measurements revealed whether a given infant was developing normally, and, for those with disorders, whether the clinical status was improving or deteriorating. The ABR method, which is noninvasive and performed during natural sleep, provided useful diagnostic information about every infant tested.