The purpose of this study is to determine the effect of bifeprunox or risperidone on the body weight of patients with schizophrenia.

Inclusion criteria:

• Current treatment of at least 3 months with risperidone.
• Primary diagnosis of schizophrenia.
• Total Positive and Negative Symptoms Scale (PANSS) score < or = 70 at screening and baseline.

Exclusion criteria:

• Psychiatric diagnosis other than schizophrenia as assessed by the modified Mini International Neuropsychiatric Interview (MINI) and considered by the investigator to be the primary psychiatric diagnosis.
• History or presence of clinically significant cardiovascular, endocrine, hepatic, renal or other medical disease that might be detrimental to the subject or confound the study.
• History of any suicide attempt within 3 years of day 1 or significant immediate risk of violence or suicidality.