Noninvasive diagnostic imaging methods to establish the efficacy of angiostatic therapies are becoming increasingly important with the first Food and Drug Administration approvals of such agents. Magnetic resonance molecular imaging is an imaging technique that allows the visualization of pathological processes in vivo with a better spatial resolution as compared with nuclear methods, such as photon emission tomography and single photon emission computed tomography. In this study, we used v3 targeted bimodal liposomes to quantitate angiogenesis in a tumor mouse model with magnetic resonance imaging (MRI) and to evaluate the therapeutic efficacy of the angiogenesis inhibitors anginex and endostatin. The MRI findings were validated with fluorescence microscopy and showed a very good correlation with the microvessel density. In conclusion, this study provides evidence that molecular MRI can be used to noninvasively measure the efficacy of angiogenesis inhibitors during the course of therapy.--Mulder, W. J. M., van der Schaft, D. W. J., Hautvast, P. A. I., Strijkers, G. J., Storm, G., Mayo, K. H., Griffioen, A. W., Nicolay, K. Early in vivo assessment of angiostatic therapy efficacy by molecular MRI.