Some cancer cell lines release soluble factors that activate the endothelial cells in vitro; also endothelial activation in vivo includes an increased expression of adhesion molecules on the apical membrane, and an increased permeability, which may contribute to the extravasation process of circulating cells. We have adapted the Miles assay into a protocol that uses IgE/antigen complex and VEGF-1 as controls. The Miles assay comprises the intradermic injection of a pro-inflammatory agent into the skin and the intravenous introduction of a dye; the increase in vascular permeability will allow for the extravasation of the dye and thus the skin will be stained. The dye is then extracted from the dissected skin and quantified by spectrophotometry. The use of localized treatments will allow for testing a larger number of experimental samples in the same animal. With this model, the effects of tumoral soluble factors (TSFs) on endothelial permeability can be studied, as well as the signaling pathways involved. It can also serve to study the interactions between endothelial, immune, and cancer cells during the extravasation process.