We investigated the selection criteria of moose, Alces alces (L., 1758), feeding on two willow species, Salix phylicifolia L. and Salix myrsinifolia Salisb., and whether these willows respond chemically. We correlated winter twig browsing with the concentrations of primary and secondary plant compounds in twigs and new leaves. Furthermore, we investigated 12 specific phenolics in twigs of S. phylicifolia. During winter, moose browsed twigs with low concentrations of phenolic compounds. Additionally, we found significant negative correlations between browsing and the concentration of 7 of the 12 specific phenolic compounds in S. phylicifolia. Most importantly, even though ours was a field study and had many potential sources of variation, a multivariate analysis revealed that these specific phenolics predicted 47% of the variation in moose browsing. The two willows reacted in different chemical ways to moose browsing, but both showed signs of defensive response in early spring and compensation growth in summer. Our data demonstrate the importance of plant secondary chemicals for feeding behaviour of moose and underline the importance of working at a species level in studies of plant-animal interactions, especially with the chemically heterogeneous willows.