Debrisoquine 4-hydroxylase (CYP2D6) is a cytochrome P450 enzyme involved in the metabolism of most neuroleptics, which are the drugs of choice for the treatment of psychotic symptoms. CYP2D6 in the brain was suggested to be functionally similar to the dopamine transporter, thus possibly influencing a neurotransmitter system involved in schizophrenia. Swedish schizophrenic patients (n = 124) and control individuals (n = 85) were investigated for two CYP2D6 polymorphisms, responsible for approximately 90% of mutations leading to poor debrisoquine metabolism. No significant CYP2D6 allele or genotype difference was found between schizophrenic patients and control individuals. Taken together with previous results, no major effect appears to be caused by the CYP2D6 gene on schizophrenia.