Using a duplex polymerase chain reaction (PCR) system, we successfully amplified GATA microsatellite loci Y-27H39 and HPRT on the Y and X chromosomes, respectively, and detected their alleles with a digoxigenin-labeled (GATA)6 probe. Among 450 unrelated Japanese including 225 females, we found 6 HPRT alleles ranging from 155 to 175 nucleotides with a simple repeat structure comprising 11 to 16 repeats. The duplex PCR is highly informative in Japanese.