Inclusion Criteria:

1. Age 18-65;
2. DSM-IV-TR diagnosis of schizophrenia, schizoaffective disorder, or bipolar disorder;
3. Patients who, in the clinical judgment of the investigator, may benefit from a switch to olanzapine;
4. Females must be of non-child bearing potential (i.e., surgically sterilized, or at least one year post-menopausal) or on an appropriate dose of oral/depot contraceptives or using barrier protection and not breast-feeding. Females must have a urine pregnancy test at screening;
5. Willingness and ability to take medications nightly at 10:00 p.m.; and
6. The subject or his/her legal representative must provide informed, written consent.

Exclusion Criteria:

1. Females who are pregnant or lactating;
2. Concurrent participation or participation within the prior 30 days in any study involving investigational medications;
3. Current (within the prior 30 days) diagnosis of substance abuse or dependence;
4. Use of olanzapine within the prior three months;
5. History of allergy or intolerable side-effects to olanzapine in the past;
6. History of significant head trauma, defined as head trauma resulting in loss of consciousness for more than five minutes and/or neurological or cognitive sequelae;
7. Evidence of any clinically relevant disease (e.g., renal or hepatic impairment, significant coronary artery disease, cerebrovascular disease, or cancer) or any clinical finding that in the opinion of the investigator could potentially be negatively affected by study participation or that could potentially affect study participation is criterion for exclusion from the study;
8. Use of fluvoxamine, nifedipine, or warfarin for 30 days prior to Baseline Visit.