Chem. synthesized chlorotoxin (TM601) has been studied as a tumor targeting peptide.In this study, the anti-angiogenic properties of TM601 are reported.Materials and Methods: In vitro and in vivo models of angiogenesis and tumor growth were used to characterize the anti-angiogenic effects of TM601.Results: TM601 bound to proliferating vascular endothelial cells, decreased human umbilical vein endothelial cell (HUVEC) invasion, and reduced secretion of bioactive matrix metalloproteinase-2 (MMP-2).Using the chick chorioallantoic membrane assay (CAM), TM601 inhibited angiogenesis stimulated by any of eight pro-angiogenic factors, and when TM601 was co-administered with bevacizumab, the combination was significantly more potent than a ten-fold increase in bevacizumab dose.TM601 did not alter tumor or vascular endothelial cell growth in vitro, but TM601 treatment of tumors grown on the CAM decreased tumor growth and intra-tumoral Hb levels.I.v. injected TM601 was also shown to significantly decrease new blood vessel growth in mice.Conclusion: TM601 inhibits angiogenesis stimulated by many factors and potentiates the anti-angiogenic effect of bevacizumab.