• The change in the total score of the Positive and Negative Syndrome Scale for Schizophrenia (PANSS) from the beginning to the end of the double-blind treatment period or to the last post-randomization assessment.
  

• The investigator's Clinical Global Impression of the Severity (CGI-S) of schizophrenia and rating of mental function on a Personal and Social Performance Scale (PSP). Evaluations of adverse events, laboratory tests, and other measures of drug safety.
  

This is a randomized, double-blind, placebo-controlled, parallel-group, multicenter, dose-response study of patients who have a Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM IV) diagnosis of schizophrenia. The duration of the study is approximately 14 weeks, including a screening period of 1 week and a 13-week double-blind treatment period. Efficacy and safety will be evaluated periodically throughout the study. Samples for pharmacokinetic evaluation will be collected at designated time points, and a blood sample will be collected at baseline (before the start of double-blind treatment) for an optional pharmacogenomics (genetics) analysis. The hypothesis is that the 3 fixed doses of paliperidone are each more efficacious than placebo in treating subjects with schizophrenia. The effectiveness is measured primarily by the change in the Positive and Negative Syndrome Scale for Schizophrenia (PANSS), and secondarily, by the investigator's Clinical Global Impression of Severity (CGI-S) and by the investigator's evaluation of the patient on a Personal and Social Performance (PSP) Scale.

Four injections of paliperidone palmitate 50, 100, or 150 milligrams equivalent administered in the gluteal muscle (buttocks). Injections will be given on Days 1, 8, 36, and 64 of the double-blind treatment period of the study.