The cause of the silent allele at D19S433 was identified as a G to A point mutation at the reverse primer binding site of the reverse primer in the Identifiler kit. Using the authors’ method for detecting the silent allele at the D19S433 locus, the frequencies of its presence in 176 people from Shizuoka (Honshu) and 156 people from Okinawa was 0.0114 and 0.0128, respectively. Thus, it is anticipated that an “apparent opposite homozygosity” inconsistency at D19S433 between a child and his/her biological parents will be observed about once every 50-60 parentage tests, producing false evidence of nonparentage. Alternative primers were designed by the authors in order to amplify the D19S433 locus alleles, and they successfully detected the silent allele. The descriptions of materials and methods address DNA samples, direct sequencing, amplification for single tandem repeat (STR) analysis, electrophoresis and typing, and data analysis. A table shows the sequences of primers designed for direct sequencing and STR typing with information on primers in the Identifiler kit. 4 tables, 3 figures, and 28 references