Inclusion criteria:

All participants must:

1. Be between age 18 and 55.
2. Meet DSM-IV criteria for Schizophrenia or Schizoaffective Disorder.
3. Treated with a stabilized antipsychotic regimen (i.e., have had no change in antipsychotic medication in the previous six weeks and no change in dose for the past 30 days).

Exclusion criteria:

Participants will be excluded if they have evidence of:

1. DSM-IV criteria for substance dependence in the last 6 months or DSM-IV criteria for abuse in the past 30 days.
2. Cognitive impairment severe enough to preclude informed consent or valid responses on questionnaires. This is defined an as a score of less than 10 on the Evaluation to Sign Consent (ESC) and judged by the treating clinician.
3. Medical illness that in the view of the investigators would compromise participation in research.
4. History of polydipsia and/or hyponatremia
5. Clinically significant endocrine disorders, as judged by the PI. Abnormalities in prolactin levels and thyroid function tests associated with the use of dopamine antagonist medications will not be exclusionary.

6. Pregnancy, planning to become pregnant, or breastfeeding. In addition, women of childbearing age are required to use an effective form of birth control for the duration of the study. Effective forms of birth control include:

   • hormonal contraceptives (birth control pills, injectable hormones, vaginal ring hormones),
   • surgical sterility (tubal ligation or hysterectomy)
   • IUD
   • Diaphragm with spermicide
   • Condom with spermicide
   • Abstinence
7. Use of any drugs (prostaglandins, vasoconstricting agents or anesthetic medications, for example) that may interact with oxytocin. Justification: Avoidance of adverse interaction with oxytocin. Assessment tool(s): Clinical interview and toxicology screen
8. History of hypersensitivity to oxytocin or vehicle, i.e. propylparahydroxybenzioate, methylparahydroxybenziate, chlorbutanol hemihydrate. Assessment tool: clinical interview
9. Presence of or history of clinically significant allergic rhinitis as assessed by the PI, M.D., or Nurse.

Justification: Inflammation of nasal mucosa could interfere with mucosal absorption of intranasally administered OT. Current rhinitis from an upper respiratory infection should be resolved prior to enrollment in study.