AIM:To elucidate the association of Epstein-Barr virus (EBV)with colorectal tumors and to demonstrate whether infectionof EBV existed in different stages of colorectal tumors involvesin the carcinogenesis.METHODS:One hundred and thirty paraffin-embeddedtissues of colorectal tumors were classified into 5 groups:26 adenomas,23 adenomas complicated with dysplasia,22adenomas complicated with carcinomatous,36 coloncarcinoma and 23 HNPCC,were examined by PCR,IHC andISH,respectively.RESULTS:EBV DNA was detected by PCR in 26 cases outof the 130 specimens,including 5 cases of adenomas,5adenomas complicated with dysplasia,5 adenomascomplicated with carcinomatous,7 colorectal carcinoma and4 HNPCC.IHC detection showed the expression of LMP1 in7 cases,including 1 adenoma,1 adenoma with dysplasia,1HNPPC,2 adenomas complicated with carcinomatous,and2 colorectal carcinomas.The expression of EBER1 detectedby ISH was positive in 6 cases,including 1 adenoma withdysplasia,2 adenomas complicated with carcinomatous and3 colorectal carcinomas.There were no significant differencesamong the results of PCR,IHC and ISH in the 5 groups.Inall cases of HNPCC,none of the tumor cells showed positivesignals of EBER1,but some EBV-positive tumor infiltratinglymphocytes were found in 2 of 23 cases.CONCLUSION:Our results showed that infection of EBVexists in human colorectal tumors,which indicates that EBVmay be involved in the carcinogenesis of colorectal tumorsbut does not play an important role.The mechanisms needto be clarified further. AIM: To elucidate the association of Epstein-Barr virus (EBV) with colorectal tumors and demonstrate that whether infectionof EBV existed in different stages of colorectal tumors involves in the carcinogenesis. METHODS: One hundred and thirty paraffin-embeddedtissues of colorectal tumors were classified into 5 groups: 26 adenomas, 23 adenomas complicated with dysplasia, 22a adenomas complicated with carcinomatous, 36 coloncarcinoma and 23 HNPCC, were examined by PCR, IHC andISH, respectively.RESULTS: EBV DNA was detected by PCR in 26 cases out of the 130 specimens, including 5 cases of adenomas, 5adenomas complicated with dysplasia, 5 adenomascomplicated with carcinomatous, 7 colorectal carcinoma and4 HNPCC.IHC detection showed the expression of LMP1 in7 cases, including 1 adenoma, 1 adenomas with dysplasia, 1HNPPC, 2 adenomas complicated with carcinomatous, and2 colorectal carcinomas The expression of EBER1 detectedby ISH was positive in 6 cases, including 1 adenoma withdysplasia, 2 adenomas complicated with carci nomatous and 3 colorectal carcinomas. Having no significant differences among the results of PCR, IHC and ISH in the 5 groups. all cases of HNPCC, none of the tumor cells showed positive signals of EBER1, but some EBV-positive tumor infiltrating lymphocytes were found in 2 of 23 cases.CONCLUSION: Our results showed that infection of EBVexists in human colorectal tumors, which indicates that EBV may be involved in the carcinogenesis of colorectal tumors but does not play an important role. Mechanisms need to be clarified further.