RIS is a new atypical neuroleptic agent widely used in treatment of schizophrenia and related disorders. It is sometimes used in serious childhood disorders as well, such as autistic disorder. It has a beneficial effect on both positive and negative symptoms of schizophrenia, accompanied by a much lower incidence of adverse effects (e.g. parkinsonism, tardive dyskinesia, dystonias, neuroleptic malignant syndrome). RIS is also used as a treatment of children with pervasive developmental disorders (PDD). RIS is metabolized to 9-OH-RIS by hepatic CYP2D6 which exhibits genetic polymorphism. Since RIS and 9-OH-RIS are equally potent, the clinical significance of CYP 2D6 status is negligible. However, in extensive metabolizers (EM) the T(1/2) or RIS is about 3 hrs and taht of 9-OH-RIS is approximately 20 hrs. In poor metabolizers (PM) the half life of RIS is about 17 hrs and that of 9-OH-RIS 23 hrs.