Vascular endothelial growth factor (VEGF) is known as an angiogenic factor for tumor angiogenesis. We developed a neutralizing anti-VEGF monoclonal antibody (MAb), MV833, and examined its antitumor activity against 27 human tumor cell lines transplanted in nude mice. All the tumor cell lines used in this study secreted various amounts of VEGF into culture medium in vitro. However, the growth of the cell lines, including three which expressed VEGF receptor, was not affected by exogenously added MV833 in vitro. All tumor cell lines including colon, lung, breast, pancreas, and melanoma, grew subcutaneously in nude mice. The growth of HeLa/v5, which had been transformed by human VEGF121 gene and secreted large amounts of VEGF, was significantly faster than that of the control vector transformant. Although the amounts of VEGF secreted from two HeLa transformants differed greatly, MV833 completely inhibited the growth of both tumors. Moreover, the growth of the other 25 human tumor cell lines transplanted into nude mice was also strongly suppressed by MV833. Neither the amount of VEGF secreted from each tumor cell line in vitro nor the expression of VEGF receptor correlated with the antitumor activity of MV833. MV833, administered when tumor volumes reached 400 mm3, completely inhibited the growth of some tumor lines. The results show VEGF to be a critical angiogenic factor for many tumors. VEGF-neutralizing antibody could be applicable as an antitumor agent for a wide range of tumors.