We discuss energetic particle and solar wind plasma data for the period around the large geomagnetic storm of November 24--25, 1978. The storm was clearly caused by an ejecta interacting with a corotating high-speed stream. We conclude that there are no data to support the attribution of this storm to specific solar activity as previously suggested. This case study illustrates the important role of energetic particles in making correct associations between solar and interplanetary phenomena. Even if there had been an identifiable source region for the ejecta, the intensity of the geomagnetic storm resulted from the interplanetary interaction. Thus predictions of the strengths of such storms cannot be based on solar observations alone but also require knowledge of stream interactions.¿ 1997 American Geophysical Union