Amplification of the human dopamine transporter gene (DAT1) was performed by the polymerase chain reaction, and polymorphism of the VNTR locus was analyzed in a population sample of 176 randomly selected Japanese individuals. Genomic DNAs were extracted from whole blood, and the 3' untranslated region of the human DAT1 gene was amplified. The amplification products were distinguished by agarose gel electrophoresis, and visualized directly by ethidium bromide staining. In this way, four alleles were visualized directly and designated A, B, C, and D in decreasing order according to size. The relative frequencies of DAT1 allels A through D were 0.0171, 0.0625, 0.9119, and 0.0085, respectively. Evidence of significant deviations from the Hardy-Weinberg equilibrium was observed from these Japanese population data. The DAT1 locus was estimated to have a heterozygosity index of 13% and polymorphic information content of 0.16.