The genetic differences of the allele frequency distributions for six STR loci (D20S480, D6S2439, D6S1056, D9S1118, D4S2639, and D17S1290) among regions in Japan were examined using our recently designed hexaplex amplification and typing system, "Midi-6" newly named, to construct a database in the Japanese population. Genotypes at six loci were analyzed in 198, 200, 175, and 196 individuals from the area of Akita, Nagoya, Oita, and Okinawa, respectively, in Japan. The allele frequency distributions were significantly different (p<0.05) at from one to five loci among the four populations when compared pairwise. Significant differences were also observed at two or three loci between Oita- or Okinawa-Japanese and the "pooled" population (n=769), respectively. However, since F(ST) (theta) values were extremely low (<0.05), ranging from 0.0020 to 0.0118 for six loci, genetic differentiation within the pooled Japanese population was negligible. Therefore, it suggested that the data of the allele frequencies at six loci in the pooled population would be employed as the base of calculation for statistical probabilities.