To determine a possible function of histone modifications in stomach carcinogenesis, we analyzed global and MGMT-promoter levels of di-methyl-H3-K9, di-methyl-H3-K4 and acetyl-H3-K9, as well as MGMT DNA methylation and mRNA expression following treatment with 5-aza-2' -deoxycytidine and/or Trichostatin A. We found that histone H3-K9 di-methylation, H3-K4 di-methylation, H3-K9 acetylation and DNA methylation work in combination to silence MGMT. The results indicate that histone modifications as well as DNA methylation may be involved in stomach carcinogenesis. In addition to its effect on DNA methylation, 5-aza-2' -deoxycytidine can act at histone modification level to reactivate MGMT expression in a region-specific and DNA methylation-dependent manner.