PET imaging with [carbon-11 (11C)]-raclopride provides an in vivo measure of dopamine D2 receptor occupancy during ziprasidone treatment and will be used to assess the relationship between ziprasidone's D2 occupancy and measures of WM and cognition. It is hypothesized that moderate D2 occupancy is associated with clinical improvement and the degree of occupancy will be correlated with WM performance. The [11C]-raclopride studies will be performed in a subset of 30 patients after twelve weeks of ziprazidone treatment. As [11C]-raclopride studies of the D2 receptor have consistently shown comparable levels of binding in controls and untreated patients with schizophrenia (e.g. Farde et al.1990), the treated patients can be compared to the untreated controls. We are using this approach because it may not be feasible to scan the patients in the unmedicated state. It is extremely difficult to justify a two to four week drug free period that would be needed to assess baseline D2 receptor availability.