We are proposing to carry out a controlled double-blind trial, using TBZ off-label in patients with schizophrenia or schizoaffective disorder only partially responsive to antipsychotics. We feel that the choice of this approach is empirically sound and, in fact, offers advantages to the more common approach of adding several antipsychotics. Our decision to maintain out focus on the dopaminergic system arises from the growing body of evidence that dopamine blockade, particularly at the level of the D2 receptor, is central to antipsychotic activity, in combination with the lack of current evidence supporting the distinct advantages of incorporating other systems.