The human genome contains a large number of tandemly repeated sequences occurring sporadically throughout the genome. The number of repetition as well as the size of the repeat sequence vary widely presumably because the tandem repeats do not encode anything. These hypervariable genetic loci due to the variable tandem repeats show high heterozygosity and frequently two distinct bands are observed upon gel electrophoresis when an indivisual`s genomic DNA is examined after PCR. We noticed that the alleles of the tandem repeats segregate from each other even though the two alleles are almost identical in sequence through the denaturation and renaturation cycles of PCR. Taking advantage of such segregation, the alleles of tandem repeats could be easily identified without resorting to gel electrophoresis but by reverse dot-blotting in which the standard DNAs of each allele are fixed on the membrane and the amplified sample is applied for the selective hybridization. [Supported by a grant from the Inje Foundation]