To investigate the relationship between 48 bp variant number tandem repeat polymorphism in dopamine D4 receptor gene and response to clozapine in schizophrenic patients, the authors included 81 inpatients with a DSM-IV diagnosis of schizophrenia and patients meeting criteria for refractory to treatment were excluded. This study found that the frequencies of five 48 bp repeats homozygous genotype and five 48 bp repeats allele were significantly less in the responders than the nonresponders, which divided by improving total schizophrenic symptom. The results of this study suggest that inherited variants of D4 may explain some of the interindividual variation seen in patient response to clozapine.