Plasma free 3-methoxy-4-hydroxyphenylglycol (pMHPG) was measured in 19 patients with acute schizophrenia before and after neuroleptic therapy. Plasma antinoradrenergic activity (pANA) of the neuroleptics used was measured after treatment. Before treatment, pMHPG was higher in the patients than in 20 normal controls. There was a positive correlation between pMHPG level and the global severity of positive symptoms. After neuroleptic therapy, pMHPG was reduced, and there was a significant correlation between the decline in pMHPG and the improvement in positive symptom score. The decline in pMHPG was also correlated with pANA. These results suggest that there is a dysfunction of the noradrenergic system in the brains of some acute schizophrenics with mainly positive symptoms, and that this dysfunction may be improved, along with positive symptom score, after neuroleptic therapy.