Exosomes are secreted membrane vesicles (30-100 nm in diameter) that form inside intracellular multivesicular bodies (MVBs) and are released upon fusion of these MVBs with the plasma membrane. When exosomes were first discovered they were thought to be nothing more than cellular waste containers, but it is now thought that the integral membrane proteins, soluble proteins, and nucleic acid contained within exosomes can be taken up by cells and influence their function. The specific contents of exosomes appear to be as diverse as the cell types that secrete them and researchers have utilized Proteome Profiler™ Antibody Arrays from R&D Systems to analyze the contents of exosomes.* The role of exosomes in intercellular communication is now being explored in many areas of research, including immune responses, cancer promoting pathways, the nervous system, and stem cells. There is also interest in utilizing exosomes as biomarkers. The potential power of exosomes as biomarkers is due to the enrichment of highly selected markers – which are less than .01% of the body fluid proteome – that occurs during exosomal sorting. This enrichment process could aid in the discovery of relatively low abundance biomarkers that would go undetected in whole fluid samples. The fact that exosomes are released in easily accessible body fluids such as blood and urine further makes them ideal as a non-invasive diagnostic tool. The utility of exosomes as biomarkers is being investigated for several diseases and pathologies, including cancer, neurodegenerative diseases, viral infection, and kidney-related diseases.