It is generally assumed that noun–noun (NN) compounds in English are stressed on the left-hand member (e.g. cóurtroom, wátchmaker). However, there is a considerable amount of variation in stress assignment (e.g. silk tíe, Madison Ávenue, singer-sóngwriter), whose significance and sources are largely unaccounted for in the literature. This article presents an experimental study in which three competing hypotheses concerning NN stress assignment are tested. The stress patterns of novel and existing compounds, as obtained in a reading experiment with native speakers of American English, were acoustically measured and analyzed. The results show that there is indeed a considerable amount of variation in stress assignment, and that all three hypothesized factors, i.e. structure, semantics, and analogy, are relevant, though to different degrees. On a theoretical level, the findings strongly suggest that a categorical approach cannot be upheld and that probability and analogy need to be incorporated into an adequate account of stress assignment in noun–noun constructions. The article also makes a methodological contribution to the debate in showing that experimental studies using pitch measurements can shed new light on the issue of variable compound stress.