Subjects may be inpatients or outpatients. All subjects will be treated throughout the study with clozapine, at a dose of 400 mg or more, unless limited by side effects. After screening, subjects will be augmented with placebo for 7 days. Any subject with a reduction in PANSS total score of 20% or greater will be discontinued from the study. Beginning on day 8, subjects will be randomized to continued augmentation of clozapine with placebo, or to augmentation with risperidone. The initial daily dose of risperidone will be 1.0 mg, increased in 1.0 mg increments to a total of 3.0 mg/day over a two week period. Subjects unable to tolerate at least one tablet of study medication will be dropped from the study. At the end of 8 weeks following randomization, at the choice of the investigator, open-label risperidone augmentation can be started.