Abstract: A metering pump comprises a diaphragm chamber with a diaphragm, a suction conduit connecting the diaphragm chamber with a metering agent tank, a pump cylinder defining a cylinder space and having an inlet connected to the diaphragm chamber and an outlet connected to a metering point through a metering conduit, and a metering piston in the pump cylinder. The metering piston is formed as a hollow tubular piston which comprises an annular seal disk at the side thereof opposite to the metering conduit. The cylinder space is defined by a stop ring and an actuating tappet movingly passes therethrough. At the beginning of a suction stroke the seal disk sealingly abuts the stop ring but allows the metering agent to pass through during the further movement of the tappet. The metering piston in no position thereof emerges from a compression ring.