In view of the central side effects of beta‐adrenoceptor blocking agents and their alleged antipsychotic action in the absence of DA receptor blockade, it is important to establish which neurotransmitters are likely to be involved. Previous animal and patient studies have, however, produced conflicting data on this point. The changes in CSF HVA, 5HIAA and MHPG during treatment with propranolol (960 mg/day) in chronic schizophrenic patients were monitored on four occasions over 30 days. Clinical changes were monitored by the Wing and Krawiecka Scales and motor activity was assessed by pedometer. CSF HVA levels were significantly increased by propranolol and the rise continued throughout the 30 day period. There were no significant changes in the other metabolites. There was no evidence of any therapeutic benefit from propranolol treatment in these patients. These findings may explain the central side‐effects and occasional reports of schizophreniform psychosis after propranolol, since an increase in DA turnover occurs without DA receptor blockade.