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It has proved difficult to find strong and replicable genetic linkages for complex diseases, since each susceptibility gene makes only a modest contribution to onset. This is partly because high-efficacy genetic markers are not usually available. The aim of this article is to explore the possibility that the total number of tandem repeats in one STR locus, rather than the frequencies of different alleles, is a higher efficacy quantitative genetic marker. DNA samples were collected from schizophrenic patients and from a control population. Alleles of the short tandem repeats (STR) loci D3S1358, vWA, and FGA were determined using the STR Profiler Plus PCR amplification kit. The two groups did not differ statistically in the frequencies of alleles at the D3S1358, vWA, or FGA loci. However, a significant difference was obtained in the vWA locus when the total number of core unit repeats was compared between the schizophrenia and control groups (33.28 ± 2.61 vs. 32.35 ± 2.58, P < 0.05). It seems that the number of STR repeats may be a new, quantitative, and higher efficacy genetic marker for directly indicating genetic predisposition to complex hereditary diseases such as schizophrenia.