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Auditory brain stem response (ABR) spectral content was analyzed for 25 normal subjects and 70 comatose, severely head-injured subjects. The normal ABR spectrum was characterized by energy peaks in three main regions: 0 to 200 Hz, 500 to 600 Hz and 900 to 1000 Hz. Head-injured subjects, in contrast, showed less overall ABR spectral energy. Even head-injured subjects with normal ABR interwave latency values had reduced spectral energy in comparison to the normal group. Among these subjects, there were differences in spectral content for subjects with good neurologic outcome versus those who died within 2 weeks post injury. Finally, head-injured subjects with abnormal interwave latency intervals typically showed distinctive spectral patterns. This subject group demonstrated energy peaks in frequency regions which, for the other groups, were void of energy peaks. Rationale for further study of ABR spectral content is offered.