Vascular endothelial growth factor (VEGF) is known as a potent inducer of angiogenesis in various human cancers. Serum VEGF concentrations of colorectal cancer patients was assessed for their clinical significance as a tumor marker. Serum samples were obtained at admission from 24 healthy volunteers and 111 patients with colorectal cancer. Preoperative serum VEGF concentrations, which are significantly higher than those of healthy controls, reflect clinical stage progression, depth of invasion, liver metastasis, lymph node metastasis and lymphatic invasion. Consequently, detection of VEGF could serve as a clinically useful marker for colorectal cancer progression and metastasis independent of other markers.