Exosomes are 30-150 nm sized particles produced by all cells and were originally thought to be as a mechanism to dispose unwanted cellular material. In recent years, however, it has become clear that exosomes can be taken up from one cell to another, and they are reconsidered as a new tool for intercellular communication. It has been reported that exosomes contain various substances derived from the original cells, such as mRNAs, miRNAs, proteins, lipids, and even double-stranded DNAs. It has also been shown that specific disease-related exosomes, such as cancer-derived exosomes, are taken up by normal cells and influence cellular phenotype and change the microenvironment within the organ for promoting disease progression. In the Hoshino laboratory, we are focusing on exosomes to elucidate their possible role in the pathogenesis of various diseases.