Platelet monoamine oxidase (MAO) activity was significantly lower than
control values in a subgroup of 16 schizophrenic patients (most of whom
were paranoid) characterized by the presence of auditory hallucinations and
delusions. Platelet MAO activity was not reduced in 16 other schizophrenic
patients without auditory hallucinations. This finding suggests that
reduced platelet MAO activity is not found in all schizophrenic patients
but tends to occur in a clinically identifiable subgroup.