Polymorphism of the (CCTTT)n repeat, a short tandem repeats (STR) located in promoter region of the inducible nitric oxide synthase (iNOS) gene, was analyzed in a total of 316 Chinese healthy subjects. Twelve alleles and forty-nine genotypes were identified. Three alleles that had not been reported previously, namely 17-repeats, 18-repeats and 19-repeats, were found in Chinese population. Mendelian inheritance of the allele in a family composed of three generations was determined. Some of the observed allele frequency of this STR locus in Chinese differed significantly from that of Caucasians in England.