Despite the recent development of various radiolabelled RGD peptides for imaging the αvβ3 integrin receptor, relatively little attention has been focused on the ability of these radiotracers to monitor changes in tumour vascularity following treatment with anti-tumour therapies. Here we describe the favourable in vivo kinetics and tumour targeting properties of several novel radiolabeled RGD containing peptides that have the ability to monitor tumour vascularity non-invasively in a variety of preclinical tumor models. These tracers may reveal important information when assessing the impact of anti-tumour therapies, in particular those that predominantly target tumour blood vessels. Consequently, these radiolabelled RGD targeting agents represent a useful approach to quantify tumor vasculature, and when used alone or in combination with additional functional imaging modalities, should enhance our mechanistic understanding of how novel therapeutic strategies impact upon tumors.