Biological vesicles are nano-sized containers that transport proteins and other substances within or between cells. Most cells release so-called extracellular vesicles (EVs), which play important roles in cell-to-cell communication. EVs also are involved in diseases, however—the spreading of a tumor, for example, is sometimes stimulated by particular EVs. For the development of therapies, regulators that can inhibit the secretion of specific EVs, without severe side effects, are therefore needed. On the other hand, EVs can also be employed as therapeutic agents. For example, EVs derived from certain stem cells are known to have a therapeutic effect on damaged tissues. Therefore, regulators that activate EV secretion are also in demand. By screening a large set of biomolecular compounds, Rikinari Hanayama from Kanazawa University and colleagues have now identified 4 potential regulators (1 inhibitor and 3 activators) for EV secretion for a variety of cells.