Cytotoxic T lymphocytes are an essential part of the adaptive immune system. They patrol our body in search for antigen-presenting cells and efficiently kill them by the regulated exocytosis of cytotoxic granules at a specialized contact area, the immunological synapse. Much of the molecular mechanism of granule exocytosis is currently unclear, and I will present some recent data from our lab about a potential contribution of granule pH and endocytosis to the process of serial killing by cytotoxic T lymphocytes.