Platelet-derived endothelial cell growth factor (PD-ECGF) has been identified to be an angiogenic factor, and a close relationship between the expression of PD-ECGF and tumor development has been postulated. This study was designed to assess both the role of PD-ECGF in human colorectal polyps as well as its relationship to the expression of other oncogenes during colorectal carcinogenesis. One hundred twenty patients with colon polyps who had undergone a polypectomy were studied. The polyps were classified based on the pathological findings as nonneoplastic or sporadic adenoma. The polyps were immunostained for PD-ECGF and vascular endothelial cell growth factor (VEGF), as well as for Ki-67 antigen and p53. The correlations between expression of PD-ECGF and clinicopathologic factors were examined. PD-ECGF was expressed at significant levels only in adenomas: in 4 of the 20 polyps with severe dysplasia (20%), and in 5 of the 20 cases of carcinoma in adenoma (25%). PD-ECGF was not detected in the nonneoplastic polyps and in adenomas with low-grade dysplasia. The intensity of immunostaining for PD-ECGF in adenomas correlated with the expression of Ki-67 antigen (P < 0.001) but not with that of p53. VEGF was not detected in any types of polyps. Angiogenic factors in colorectal adenomas might play an important role in carcinogenesis. The correlated expression of PD-ECGF and Ki-67 antigen suggests that PD-ECGF might not only act as an angiogenic factor, but also as a tumor growth factor.