The brainstem auditory evoked response (BAER) was evaluated as an aid in the early diagnosis and prognosis of 17 comatose blunt head-injury patients. Click stimuli (60 dBSL, 10/sec) were presented monaurally through headphones. BAER's were recorded between Cz and ipsilateral mastoid; contralateral mastoid ground. No BAER waves occurred in three "brain-dead" patients. Two patients with initially abnormal BAER's did not show improvement in followup recordings, and died of their brain injuries. Recovery occurred in 12 patients with normal followup BAER's, regardless of whether initial BAER's had been abnormal (three patients) or normal (nine patients). Apparently, initial BAER's (mean, 31 hours postinjury) can be abnormal as the result of reversible damage. Followup BAER's (3 to 6 days postinjury) did correspond with patient outcome at a time when clinical prognoses were often uncertain. BAER's aided diagnostically in determining the extent of brainstem damage and the effectiveness of treatment.