Objective To investigate the expression of guanylyl eyelasec(GC-C)mRNA in pefipheral blood of colorectal cancer patients and discuss its clinical significance. Methods To detect the GC-C mRNA in peripheral blood of colorectal cancer patients by reverse transcriptase PCR and analysis their clinical and pathological indexes. Results The positive rate of GC-C mRNA in 52 colorectal cancer patients was 50%(26/52),while to patients with extra-intestinal cancer,the positive rate was 0(0/8).There were significant difierences of positive rate of GC-C mRNA associated with tumor infiltration(P＜0.05)and tumor embolus in vessel(P＜0.05).While to CEA level in peripheral blood(P＞0.05),but there were no statistical difference.The positive rate of micrometastasis in coloreetal cancer patients might increase using the GC-C mRNA combined with CEA level in peripheral bood.The positive rate of GC-C mRNA in colorectal cancer patients with Dukes A、B、C and D stages were 0(0/3),47.06%(8/17),52.38%(11/21),63.63%(7/11),The expression of GC-C mRNA increased with the clinical stage chang,there was no statistical difference.Conclusions GC-C expresses selectively in peripheral blood of colorectal cancer patients.Itis a valuable new tumor marker in micrometastasis diagnosis and post-operation follow-up of colorectal cancer,and it can also be used as the location determination of metastasis intestinal tumor.