Risperidone, a benzisoxazole derivative, is a novel antipsychotic agent that has an extremely strong binding affinity for serotonin 5-HT2 receptors, a strong binding affinity for dopamine D2 receptors, and a high affinity for alpha 1- and alpha 2-adrenergic receptors and histamine H1 receptors. Its affinity for serotonin receptors is approximately 200 times greater than that of haloperidol, and its dopamine antagonistic potency is comparable to that of haloperidol. Its major metabolite, 9-hydroxyrisperidone, has similar pharmacologic activity, and thus the parent compound and metabolite form the active antipsychotic moiety. Clinical trials demonstrate that risperidone is an effective antipsychotic agent that improves negative as well as positive symptoms of schizophrenia. At recommended dosages, the frequency of extrapyramidal side effects is no greater than that seen with placebo. The drug appears to be an advance in the treatment of psychoses.