 Male or female patients aged 18-60 years suffering from schizophrenia or schizoaffective disorder will be eligible to participate in this study Visit 1. Following the baseline clinical assessments Visit 2, previous antipsychotics will be discontinued while initiating ziprasidone at 20mg BID and subsequently increasing the dose to 60mg BID Visit 2-4. For patients already treated with ziprasidone 60 mg BID, no titration will be necessary. If patients are on a lower dose, they will only be included in the study if the treating clinician recommends an increase of the dose to 60 mg BID. Participants will undergo a total of 3 raclopride PET scans 6, 12, and 24 hours postdose Visits 5-7 after they have been on ziprasidone for at least 14 days. Psychopathology and side effects will also be assessed on these PET visits. MRI scan will be completed when possible Visit 8. In the subsequent 6-month follow-up phase Visit 9-17, participants will have clinical assessments biweekly in the first 3 months and monthly in the following three months. The dose will be titrated according to clinical response and tolerability in an open-labeled manner to a maximum dose of 80 mg BID. 