Specific Aims - We propose a double-blind, placebo-controlled trial to study the effectiveness and tolerability of adding risperidone to stable yet only partially remitted patients with schizophrenia maintained on clozapine. We anticipate enrolling a total of 40 subjects over a period of two years at the Freedom Trail Clinic and affiliated sites in Boston, Massachusetts. Our primary outcome measure will be change in total score on the Positive and Negative Syndrome Scale (PANSS). Secondary hypotheses are (1) that the clozapine-risperidone combination is well tolerated, (2) that clozapine levels will not be influenced by risperidone, and (3) that prolactin elevation is suitable as a surrogate marker of sufficient D2 blockade to predict response.