Abstract: Purpose : To investigate the polymorphisms of exons 1 ～ 5 in human O6-methylguanine-DNA methylt ransferase (MGMT) gene and their relationship with the susceptibility to tumors. Methods : The poly- morphisms of exons 1～5 were analyzed with polymerase chain reaction (PCR)-single st rand conformation poly-morphism (SSCP) and DNA sequencing in 188 Chinese Han people (100 healthy people and 88 tumor patients) .Results : A polymorphism of exon 3 , a C-to-T missense mutation , was detected at the first base of codon 84 (CTT →TTT , Leu →Phe) , and a polymorphism of exon 4 , a C-to-T same sense mutation , was found at the third base of codon 94 ( TTC →TTT , both encode Phe) . There was no statistical significance of the polymor- phisms of the two sites between the two groups ( P < 0. 05) . Besides , there was a missense mutation of exon 5 in the tumor people , that is , a G-to-C change of the second base at codon 200 ( GGC →GCC , Gly →Ala) . This polymorphism didn’t exist in the normal people. Conclusion : There were the polymorphisms of exons 3 ,4 and 5 in MGM T gene. The relationship between the polymorphism of exon 3 or 4 and tumorigenesis might be weak. The polymorphism of exon 5 only existed in the tumor people , which indicated that the polymorphism might be correlated with carcinogenesis.

Key words: O6-methylguanine-DNA methylt ransferase, genetic polymorpbism, tumor