Acetylcholine is an old neurotransmitter that does not only work in the nervous system. The vital molecule controls many bodily functions, in particular interaction with the environment. It sets barriers and regulates their permeability, for example that of skin and lungs and during the intake of food. It is also a component with a decisive impact on the functioning of the immune system – and can, conversely, be involved in the incidence of illnesses. How exactly does acetylcholine work? What forms are taken by the disorders that lead to illnesses? How can this knowledge be applied? From fundamental research to clinical studies – the researchers in the LOEWE research cluster are focusing on the molecule’s non-neuronal areas of activity.