• Autonomic nervous system (ANS) activity in acute schizophrenic patients was assessed to examine predictive relationships to clinical course. Unmedicated patients were rated on global psychopathology and tested on skin conductance, heart rate, and skin temperature during rest, a series of tones, and reaction time and mental arithmetic tasks three weeks after admission and again about three months later. On the admission tests, a pattern of ANS activity found in schizophrenics in general (high resting "arousal," slow habituation, and attenuated ANS reactivity, particularly to demanding stimuli and situations) was found in patients who were to remain clinically ill but not in patients whose recovery was more complete, especially in males. Thus, ANS activity is predictive of short-term outcome in acute schizophrenia. Minimal ANS changes accompanied clinical improvement, which suggests a "trait" interpretation, but "state" effects cannot be completely ruled out.