Hypoxia-inducible factor 1 (HIF-1), a transcription factor, is overexpressed in common human cancers and their metastases. This study aimed at determining the expression levels of HIF-1alpha and vascular endothelial growth factor (VEGF) in SW480 cells and in colorectal adenocarcinoma tissue and ascertaining whether HIF-1alpha and VEGF play important roles in tumor angiogenesis.HIF-1alpha mRNA expression was analyzed using in situ hybridization and RT-PCR. HIF-1alpha and VEGF protein were detected in SW480 cells and colorectal adenomas and adenocarcinomas by immunohistochemistry using streptavidin/peroxidase (SP). Western blot was used to detect HIF-1alpha protein extracted from SW480 cells. Microvessel density (MVD) in colorectal carcinomas was determined by anti-CD34 immunostaining in colorectal carcinomas.Optical density values representing HIF-1alpha mRNA expression levels were found to be significantly higher in SW480 cells in hypoxic conditions than in cells under normoxic conditions (P0.05) or in hypoxic conditions but treated with genistein (P0.05). The levels of HIF-1alpha and VEGF protein expression in SW480 cells were significantly higher in the hypoxia group than in the normoxia group (P0.01, P0.05, respectively) and hypoxia/genistein group (P0.01, P0.05, respectively). The positive expression rates of HIF-1alpha mRNA changed dramatically when comparing colorectal adenomas with adenocarcinomas of different Dukes' stages (P0.05). HIF-1alpha mRNA was also expressed at higher levels in adenocarcinomas than that in adenomas (P0.01). HIF-1alpha protein expression correlated significantly with VEGF protein expression and MVD.Hypoxia induces the expression of HIF-1alpha and VEGF in colorectal adenocarcinomas. HIF-1alpha may play an important role in angiogenesis and tumor progression by regulating the expression of VEGF in human colorectal carcinomas.