<qa>  How many patients will be enrolled at each location?The study will be conducted at two sites: Manhattan Psychiatric Center MPC, and the Clinical Research and Evaluation Facility at the Nathan S. Kline Institute for Psychiatric ResearchRockland Psychiatric Center NKI. A total of 60 patients will be enrolled, 30 at each location. After a screening period of 1 week, all patients will be entering an open label, four-week quetiapine treatment period run-in phase, during which quetiapine will be titrated to 600 mg PO daily and other adjunctive antipsychotics will be gradually tapered and discontinued. Other concomitant medications such as mood stabilizers will be maintained, if their dose has been stable for the preceding 2 months. Patients not responding to quetiapine treatment at 600 mg PO defined as reduction of 15 change in Positive and Negative Syndrome Scale PANSS total score between start of run-in to end of week 4 during the run-in phase, will be eligible to enter the double blind phase. Study baseline will be Day 7 of Week 4 of the run-in phase. Patients qualifying for the double-blind phase will be randomly assigned to either high dose 1200 mg quetiapine daily Group A or to 600 mg quetiapine Group B daily and treated on the assigned dose in a double blind fashion for 8 weeks Week 1 through Week 8 of double blind phase. Measures of extra-pyramidal side effects, psychopathology, and safety will be conducted throughout the trial. 