The human dopamine transporter (DAT1) gene contains a variable number of tandem repeats (VNTR) in its 3'-untranslated region (UTR). The linkage and association between the VNTR polymorphism of DAT1 and various neuropsychiatric disorders have been reported. We have determined the genomic structure of DAT1 genes containing 7-, 9-, 10-, and 11-repeat alleles and examined the effect of VNTR polymorphism in the 3'-UTR region of DAT1 on gene expression using the luciferase reporter system in COS-7 cells. Luciferase expression was significantly higher when the 3'-UTR of the DAT1 gene contained the 10-repeat allele than when it contained the 7- or 9-repeat alleles. This suggests that VNTR polymorphism affects the expression of the dopamine transporter.