Elevated plasma vasopressin concentrations have been documented in antipsychotic drug-treated patients as well as a drug-free acutely psychotic patients. To evaluate the effects of antipsychotic drugs on plasma vasopressin, we measured vasopressin response to a single dose of intramuscular chlorpromazine or intravenous haloperidol in normal individuals and to 2 weeks of oral antipsychotics in patients with acute schizophrenia. Neither intramuscular chlorpromazine nor intravenous haloperidol affected plasma vasopressin in normals, except in one subject who developed high plasma vasopressin concentrations coincident with marked hypotension following chlorpromazine. Prior to antipsychotics, two acute schizophrenia patients had elevated plasma vasopressin concentrations, which normalized during antipsychotic drug treatment. We conclude that antipsychotics do not directly stimulate vasopressin release, but may indirectly stimulate vasopressin release by well-described baroreceptor reflex mechanisms if hypotension occurs. Also, acute schizophrenia may be associated with increased plasma vasopressin levels in some patients.