• The difference in change from baseline to the 12-week time point between bifeprunox and placebo using the Positive and Negative Syndrome Scale (PANSS). [ Time Frame: 12 weeks ] [ Designated as safety issue: No ]
  

• The difference in PANSS score at the 12-month time point between bifeprunox and quetiapine. Also, responder rate, time to response/withdrawal, global clinical assessments (CGI), assessment of depressive symptoms (CDSS) and health economic assessments. [ Time Frame: 12 months ] [ Designated as safety issue: No ]
  

Schizophrenia is a serious and disabling mental disorder that affects approximately 1% of the world's population. There are a number of antipsychotic drugs in use but none is ideal, in particular because their safety profile is complex and their effectiveness is limited. In particular, after having overcome acute exacerbations many patients continue to experience significant symptoms that prevent an adequate functioning. In the current study, patients suffering from schizophrenia and currently in a post-acute maintenance phase of the disease will be included. Non-treatment resistant patients will be included in the study, since they have partially responded to their current antipsychotic treatment but still have clinically significant symptoms and/or impairment of functioning in their daily life. The study is a 12-month study with an initial 12-week placebo-controlled, quetiapine-referenced phase. After this initial 12-week phase, the patients allocated to placebo will be switched to bifeprunox. In the final non-inferiority analysis of the 12-month data, the results from this study will be combined with the data from a similar study (11915A).