Acutely psychotic schizophrenic patients not taking tmtipsychotic medications and control subjects were studied before and during treatment with debrisoquin (DBQ), an inhibitor of monoamine oxidase, which does not penetrate into brain. Homovanillic acid (HV A) and 3-methoxy-4-hydroxyphenylglycol (MHPG) were measured in plasma, urine, and cerebrospinal fluid ((SF). Significant differences between patients and control subjects were more easily discerned during treatment with DBQ. In patients, HVA was increased in plasma but not in urine or CSF, although MHPG was increased in all three fluids. There were many significant correlations between plasma MHPG and HV A levels and clinical ratings of psychoticism. Plasma MHPG correlated positively with both the severity of positive and negative symptoms and plasma HV A correlated only with positive symptom severity. These data suggest that both dopamine and norepinephrine (NE) metabolism are disturbed in acutely psychotic schizophrenic patients; disturbed NE metabolism may relate to negative symptoms as well. [Neuropsychopharmacology 8:97-109, 1993J by the receptor blockade (Carlsson and Lindqvist 1963).In the aggregate, these initial and subsequent basic neu ropsychopharmacologic studies have led to the ''DA hy pothesis of schizophrenia or psychosis," which suggests that schizophrenia/psychosis is associated with either an increase in central nervous system (CNS) DA release or an increase in DA receptor sensitivity (for recent reviews see Davis et al. 1991;Seeman et al. 1987). Sub