Most active tumor targeting strategies focus on the specific interactions between ligands (antibodies or peptide mimetics, nucleic acids) conjugated to drug carriers and receptors expressed on tumor cells. Despite a number of exciting in vitro results, their clinical application remains challenging. One limitation of the current active tumor targeting strategies may be that they lack access to the tumor targets underlying the endothelial barrier. We aim to develop nanoparticulate drug carriers that can preferentially access tumor tissues by enhancing extravasation of the carriers through particle surface modification. The effects of surface modification on the particle flow deceleration and on the biodistribution of the particles will be examined using an in-vitro laminar flow assay and a tumor xenograft animal model, respectively.