In this search for a possible association between the dopamine transporter gene (DAT1) polymorphism and alcoholism, 655 Japanese alcoholics were grouped according to their aldehyde dehydrogenase-2 (ALDH2) genotypes. Because inactive ALDH2 is an established negative risk factor for alcoholism, alcoholics with the mutant allele, ALDH2*2, were considered a relatively homogeneous group. The frequency of the 7-repeat allele of the DAT1 variable number of tandem repeat was significantly higher in alcoholics with ALDH2*2 than in control subjects. These results are consistent with the hypothesis that alteration in the dopaminergic system plays some role in the development of alcoholism.