The etiology of non-insulin-dependent diabetes mellitus (NIDDM) is still unclear, but appears to involve some genetic factors. There have been disputes over the association between DNA sequences flanking the insulin gene and NIDDM. In order to characterize insulin gene polymorphism in the Chinese population and elucidate its association with NIDDM, 100 unrelated Chinese subjects living in Taiwan were observed for polymorphism of this hypervariable region. Most of them were descendants of immigrants from the southern part of mainland China. Among them, 52 were nondiabetic controls, and 48 were subjects with NIDDM. Insulin gene polymorphism was classified into classes 1, 2 and 3 alleles according to Bell et al. Neither the class 2 allele nor the genotype for the homozygous class 3 allele was not observed in this study. The allelic frequencies of class 1 and 3 genes were 97% and 3% in the nondiabetic subjects, and 99% and 1% in the NIDDM group, respectively. The frequencies of genotypes 1/1 and 1/3 were 94% and 6% in nondiabetics and 98% and 2% in the NIDDM group, respectively. No significant association was found between insulin gene polymorphism and NIDDM. It is concluded that DNA marker flanking the insulin gene may not be associated with the development of NIDDM in Chinese subjects.