Using aggregate data, the paper analyzes the importance of inventory investment for German business cycles since 1960. In contrast to U.S. experience, the traditional productionsmoothing/ buffer-stock model is not rejected by empirical evidence. Preliminary national accounts data of inventory investment have particularly poor quality. In order to be able to analyze recent stockbuilding trends in Germany, we propose a composite index aggregating information drawn from monthly production and sales statistics as well as from the Ifo business survey.