Six schizophrenic patients received propranolol hydrochloride to evaluate pharmacological, endocrinological, and antipsychotic properties of the drug. They had previously been unsuccessfully treated with phenothiazines. After a drug-free period of two weeks, propranolol was administered in gradually increasing doses. After two to four weeks, a low dose of phenothiazines was added. The clinical effect was evaluated using the Comprehensive Psychopathological Rating Scale. Three of the six patients showed a definite improvement with propranolol therapy given as a sole treatment. Propranolol in plasma was positively correlated to dosage. The proportion of its major metabolite, 4-hydroxy-propranolol, decreased with increasing drug dose. Melatonin and prolactin levels in serum decreased noticeably with propranolol treatment. When phenothiazines were added, prolactin increased above drug-free levels. These results support the view that propranolol has an antipsychotic potential that needs further evaluation in clinical trials.