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Background: To investigate whether a TNF-g gene polymorphism is associated with the development of insulin-dependent diabetes mellitus, we analyzed the TNF-g gene polymorphism with restriction enzyme Ncol in 38 Korean patients with insulin -dependent diabetes mellitus(IDDM) and in 150 healthy controls. Methods: Genomic DNA was extracted from white blood cells, and amplified by polymerase chain reaction(PCR) on 735 base pairs fragment of TNF-g gene with NcoI polymorpnic site. 735 bp PCR product was digested with NcoI restriction endonu- clease, then analyzed by agarose gel electrophoresis to detect the NcoI restriction fragment length poly- morphism(RFLP). The TNF-g alleles were divided into two types according to the electrophoresis patterns. TNF-b*1 allele, which contains the Ncol restriction site(CCATGG), should be digested 539 bp and 196 bp fragments. On the other hand, TNF-g*2 allele, which lacks the restriction site, only showed 735 bp fragment. Results: Six out of 38(15.8%) IDDM patients were homozygous for the TNF-b*1 allele, 11(28.9%) were homozygous for the TNF-b*2 alleie, and 21 (55.3%) were TNF-b*1/*2 heterozygous compared to 21.7%, 30.7% and 49.3%(p=0.83), respectively, in control subjects. Conclusion: The TNF-b gene polymorphism was not associated with insulin-dependent diabetes mellitus in Korean subjects.