Optical-based in vivo imaging of vascular changes and vascular leak is an emerging modality for studying altered physiology in a variety of different cancers and inflammatory states. A number of fluorescent imaging probes that circulate with the blood, but have no target selectivity, have been used to detect tumor leakiness as an indication of abnormal tumor vasculature. Inflammation is also characterized by distinct vascular changes, including vasodilation and increased vascular permeability, which are induced by the actions of various inflammatory mediators. This process is essential for facilitating access for appropriate cells, cytokines, and other factors to tissue sites in need of healing or protection from infection. This application note investigates the use of three fluorescent imaging probes, to detect and monitor vascular leak and inflammation in preclinical mouse breast cancer models.