Methods - The proposed trial will be placebo-controlled, randomized, and double-blind, and it will last 8 weeks. We expect to enroll 40 subjects overall. Subjects will be eligible if they are diagnosed with schizophrenia and treated with clozapine. In addition, they must have residual symptoms of schizophrenia as we are interested in improvement of residual psychopathology. Subjects with dementia or mental retardation as well as pregnant women will be excluded. After a 2-week placebo lead-in period to assure stable psychopathology and minimize placebo-response, subjects will be randomly allocated to receive 6 weeks of either risperidone (20 subjects), or matching placebo (20 subjects) added onto their customary antipsychotic medication, clozapine. Overall, there are 5 study visits every 2 weeks plus the initial screening visit. On each visit, subjects will be evaluated with standard psychiatric rating scales of psychopathology and side effects. In addition, we will measure serum levels of the medications used, clozapine and risperidone.