The purpose of this study is to determine whether six months treatment with the antipsychotic medicine Seroquel (quetiapine) may affect the schizophrenic patient's glucose metabolism

Inclusion Criteria:

• In- or outpatients with schizophrenia, 18-65 years old, requiring a change in treatment due to insufficient efficacy or tolerability and giving signed informed consent.

Exclusion Criteria:

• Known diabetes mellitus, high HbA1c, fasting plasma glucose and/or high 2h glucose-OGTT.
• Previous use of atypicals (3 months) or other medications that might influence glucose metabolism
• Contraindications or non-responsiveness for any of the treatments or other safety issues
• Expected non-compliance to treatment and/or study procedures