Disclosed is a method for operating an electromagnetic flowmeter and a flowmeter. A measuring tube provided with a coil arrangement for producing a magnetic field at right angles to the direction of flow. The direction of current flow in the coil arrangement is altered periodically, and the current is kept essentially constant in one period after a rise to a predetermined value. the voltage applied to the coil arrangement and/or its derivative is determined and compared with an associated reference value. If this voltage or derivative does not fall below the reference value in a desired minimum time within a measurement period, an error message can be emitted in order to indicate a fault. If the voltage or derivative falls below the reference value, it is ensured that the magnetic field is sufficiently stable and measured values for a voltage which can be tapped off at measurement electrodes.