AIM: Cyclooxygenase-2 (COX-2) is one of the rate-limiting enzymes in metabolism of arachidonic acid, and COX-2inhibitors demonstrate preventive effects on cancer,especially on colorectal cancer. The underlying mechanism remains unclear. The aim of this study was to illustratethe relationship between angiogenesis and COX-2 in carcinogenesis of colorectal cancer.METHODS: One hundred and seventy patients with colorectal cancer were enrolled in our study from January 1993 to September 2001 in School of Oncology, Peking University. COX-2 and VEGF expression were detected with the immunohistochemistry (IHC) technique. IHC assays were carried out with the aid of tissue microarray (TMA)procedure. Specimens from 35 of these patients were examined with reverse transcriptase PCR (RT-PCR).RESULTS: COX-2 and VEGF expressions were stronger in colorectal cancer than those in the corresponding normal tissues, at both protein and mRNA levels. One hundred patients were eligible for analysis after IHC assay of COX2 and VEGF. The positive rate of VEGF was much higher in COX-2 positive group (47/85) than in COX-2 negative group (x2 = 4.181, P = 0.041). The result was further verified by the result of RT-PCR (x2= 8.517, P = 0.003). Correlationcoefficient was 0.409 after Spearman correlation analysis (P= 0.015).CONCLUSION: COX-2 may be involved in the course of tumor angiogenesis of colorectal cancer and acts through VEGF.