 Patients and matched healthy controls are examined at baseline and again after the patients have been treated for 6 months with a combined 5-HT2A- and dopamine D2- receptor blocker. We have chosen the atypical antipsychotic compound, quetiapine, for the present study since this drug is characterized by a fast kofflow affinity for the dopamine D2 receptors. The purpose of the study is to examine pathophysiological and neuropsychological mechanisms - not treatment effects. We want to characterize neurobiological and functional endophenotypes or vulnerability indicators and to study their stability over time and their relation to treatment and contemporary psychopathology. To the extent that candidate endophenotypes can be characterized as stable and independent of treatment and contemporary psychopathology they will be analysed together with similar findings from previous identicalcohorts of schizophrenic patients. Specific disturbances will also be related to candidate genes for schizophrenia. 