A group pf 19 acute, medication-free schizophrenic patients was studied, using average-evoked responses (AERs) to four intensities of light. Comparison with age- and sex-matched normal controls and patients with bipolar affective disorders showed that schizophrenics had smaller AER amplitudes and either no increase or an actual decrease in amplitude with increasing stimulus intensity. Normal subjects and schizophrenic patients were discriminated with 71% accuracy using AER variables; normals, patients with bipolar disorders, and schizophrenic patients with 64% accuracy. Patients who evidenced this AER "reducing" pattern to a noticeable extent early in hospitalization showed greater improvement and tended to have relatively good premorbid histories.