A method and an apparatus for determining the temporal curve of the voltage (ue(t)) at the electrodes (3) of a spot welding gun (1) during a spot welding process as an indicator of the welding quality, wherein the electrodes (3) are fastened to gun arms (2) that can be moved relative to each other are provided. The apparatus includes a device (9) for measuring a measuring voltage (um(t)) between the electrodes (3), that measuring device (9) being connected to measuring leads (6) extending along the gun arms (2), and further includes a compensating coil (7) for measuring a compensating voltage (uk(t)) for compensating measuring errors within measuring leads. In order to determine the temporal curve of the voltage (ue(t)) at the electrodes (3) of the spot welding gun (1) during a spot welding process as precisely as possible, the device (9) for measuring the measuring voltage (um(t)) and the device (10) for measuring the compensating voltage (uk(t)) are designed as separate units for separate detection and are connected to a device (11) for processing the detected values.