A cylinder/piston unit is disclosed for pre-fill, storage and release when desired of an active substance, such as a medicament. The cylinder/piston unit is provided with a cylinder and with a piston which is guided therein and which is sealed off in a sterile manner by a rubber seal, the cylinder and the piston enclosing a chamber that can be filled at least temporarily with active substance, and the cylinder having at least one discharge element at its front end. For this purpose, the piston resting in a rear position is sealed off relative to the cylinder in a sterile manner by a static front sealing element and by a static rear sealing element. Arranged spatially behind each static sealing element, there is a parking area for receiving the respective sealing element. When the piston is actuated, the individual static sealing elements are transferred from their respective sealing position into a parked position located in the parking area, and each sealing element in the parked position touches only the cylinder wall or only the piston wall. With the present invention, a cylinder/piston unit is developed which can be pre-filled and in which, despite a sterile sealing of the piston, only a slight force has to be applied in order to accelerate and/or move the piston.