<正>Objective: To study the correlation of the methylation of the promoters of hMLH1 and hMSH2 with microsatellite instability （MSI） in the tissues of gastric carcinomas. Methods: A total of 68 sporadic cases of gastric carcinoma were studied. Ten specimens of normal gastric mucosa served as control. Methylation of hMLHl and hMSH2 was observed with methylation-specific PCR

and MSI analyzed with PCR-based techniques. Results: No methylation of hMLHl and hMSH2 was found in 10 specimens of normal gastric mucosa. Methylation of hMLHl was detected in 11 cases （16. 2%） of gastric cancers and MSI in at least one locus was found in 17 cases （25%） of the 68 with aid of 5 microsatellite markers

in which eight were MSI-H （≥2loci showed instability） nine MSI-L （only one locus showed instability）

and fifty-one were MSS （no instability at any marker）. The frequency of methylation was significantly high in MSI-H （87. 5%） than in MSI-L （11.1%） and MSS （5. 9%）. CP<0. 01 - 0. 001) but there was no difference of methylatio