Normalizing blood flow promotes drug delivery by reducing the interstitial pressure that counteracts diffusion. However, normalizing agents can also reduce vascular permeability. Vascular permeability greatly influences the extravasation of drugs associated with carriers, including liposomes, micelles or other nanoparticles. Recent advances to manipulate vascular permeability exemplify how adjuvant therapy might facilitate the targeting of future and existing anti-cancer therapies to tumor tissues. Unfortunately, the lack of accurate means to quantify vascular permeability is a significant hurdle to predicting its direct influence on drug localization and uptake in vivo. Classically, vascular permeability has been measured using the Miles Assay. This assay determines the leakage of a visible dye from the vasculature into the surrounding tissue spectrophotometrically, with the relative vascular permeability determined as the ratio of extravasated versus intravascular dye. This assay has several limitations, however, that preclude its use in many cases. It is limited to the analysis of a single time-point, which must be selected empirically from pilot experiments. Neosperidin-dihydrochalcone Furthermore, due to the wide range of experimental approaches described in the literature, results are subject to a high degree of variability and their repeatability must be considered. Variability can be mitigated somewhat by using large tissue volumes. Consequently, these experiments are generally performed in rodent models with large group sizes, which is both expensive and timeconsuming. As the Miles assay is limited to the determination of average permeability over an entire tissue, localized differences in vascular permeability, particularly within tumors, cannot be detected. A Folic acid dynamic measure of vascular permeability would allow for the assessment of the impact of regional and temporal changes in vascular permeability on drug distribution within solid tumors. Here, we present an integrated method to visualize and quantify the real-time dynamics of dextrans in a shell-less chick chorioallantoic model. Regional and temporal differences in vessel permeability within the tumor microenvironment are captured at high resolution using an intravital imaging approach. The use of dextrans of different molecular weights allows for the concurrent evaluation of vascular permeability and vascular structural integrity.