Provided are compositions and methods that relate to prophylaxis and therapy of angiogenesis associated disease and includes novel knockin mice which express novel human/mouse chimeric endoglin, vectors for use in making such mice, and murine embryonic stem cells comprising the novel human/mouse transgene. Also provided are anti-human endoglin monoclonal antibodies (mAbs) which can be used as antiangiogenic agents for prophylaxis or therapy of human tumor angiogenesis and human angiogenesis-associated diseases having excessive vascularization. The mAbs do not cross react with murine endoglin. Also provides are methods for using the anti -human endoglin mAbs for prophylaxis or therapy of human tumor angiogenesis and for angiogenesis-associated diseases having excessive vascularization.
