The　aim　of　this　article　was　to　investigate　the　correlation　between　expression　of　O(6)-methylguanine-DNA　methyltransferase　(MGMT)　in　osteosarcoma　and　the　curative　effect　of　alkylating　agent　(Cis-diaminodichloroplatinum,　CDDP).　42　male　patients　and　34　female　patients　with　a　median　age　of　17　years　(9　to　43　years)　were　eligible　for　this　study.　According　to　histopathological　types,　there　were　3　cases　of　telangiectatic　osteogenic　sarcoma,　22　cases　of　osteoblastic,　11　cases　of　chondroblastic　and　16　cases　of　fibroblastic　sarcoma.　Immunohistochemical　method　was　used　to　detect　the　expression　of　MGMT　protein.　The　correlations　between　MGMT　expression　and　the　curative　effect　of　CDDP　on　osteosarcoma　have　been　investigated.　It　was　shown　by　immunohistochemical　staining　that　among　76　osteosarcoma　biopsy　specimens,　52　(68%)　cases　were　positive,　27　(35%)　cases　were　weak　positive,　18　(24%),　cases　were　moderate　positive,　and　7　(9%)　cases　were　strong　positive.　There　were　no　significant　differences　in　MGMT　expression　among　different　pathological　types　of　tumors　(p　＞　0.5).　After　CDDP　chemotherapy,　among　pathologic　specimens　in　which　MGMT　expression　was　positive,　necrosis　rates　were　as　follows:　grade　I,　5　cases　(38%);　grade　II,　7　cases　(25%);　grade　III,　15　cases　(21%);　grade　IV,　2　cases　(23%).　Osteosarcoma　necrosis　rate　was　low　when　the　expression　of　MGMT　protein　was　positive,　whereas　necrosis　rate　was　high　when　there　was　a　low　level　of　MGMT　expression　(p　＜　0.01).　There　was　a　significant　negative　correlation　between　the　level　of　MGMT　expression　in　osteosarcoma　tissue　and　osteosarcoma　necrosis　rate　after　cisplatin　chemotherapy.　(C)　2011　Association　of　Basic　Medical　Sciences　of　FBIH.　All　rights　reserved