Noradrenaline (NA, norepinephrine), dopamine (DA) and adrenaline (A, epinephrine) concentrations were determined by means of a specific and sensitive radioenzymatic method in plasma, CSF, and urine of schizophrenic patients and in a group of age- and sex-matched controls without history of mental disorder. NA levels were significantly increased both in plasma and CSF of schizophrenics, particularly in paranoids. The increase in plasma NA concentration can probably be ascribed to the higher unspecific arousal level of these patients, whereas the increase of CSF NA levels probably reflects a rise of central noradrenergic activity. The physiopathological significance of this overactivity is questionable.