The intermetallic compound formation in gold–aluminum thin-film couples is monitored as a continuous function of time by photographic x-ray analysis during in situ annealing in the temperature range 35°–350 °C. A copper rotating anode x-ray machine gave high enough intensities to allow phase changes to be detected in a matter of minutes. The experimental procedure will be presented. It was found that Au5Al2 is the dominant crystalline phase in the initial stage of the reaction. The order of formation of the various intermetallic compounds is discussed.