Exosomes are small membrane-bound vesicles that in recent years have emerged as important molecules for inter-cellular communication. Exosomes are produced during both normal and patho/physiological conditions, and cancer cells have been shown to secrete exosomes in greater amounts than normal cells. Alix protein, named also ALG2 interacting protein or PDCD6-interacting protein, is a cytoplasmic protein that interacts with apoptosis associated-proteins. Alix plays an active role in exosome biogenesis and it is a useful internal marker for the analysis of exosomal proteins with western blotting.