Differences in the protein content of individuals may affect their response to signals produced by opposite-sex conspecifics and how opposite-sex conspecifics respond to the individual's own signals. Many terrestrial mammals use over-marks to communicate with potential mates. In this study, we determined whether over-marking behavior is affected by the protein content of the top- and bottom-scent donors of an over-mark. We tested two hypotheses by performing two experiments on meadow voles, Microtus pennsylvanicus, in which the top- or bottom-scent donors of an over-mark were fed a diet containing either 9, 13, or 22% protein; these protein concentrations are similar to those that voles may consume in free-living populations. In experiment 1, we varied the protein content of the top-scent voles but not that of the bottom-scent donor. We tested the hypothesis that top-scent donor voles fed a diet high in protein content deposit more scent marks and more over-marks than do top-scent donor voles fed diets lower in protein content. In experiment 2, the top-scent voles were fed a 22% protein diet but the protein content of the diet of the bottom-scent donor varied. We tested the hypothesis that the top-scent donor will deposit more scent marks if the bottom-scent vole was fed a diet high in protein content than if it was fed a diet lower in protein content. Protein content of the top-scent vole's diet did not affect the number of scent marks and over-marks it deposited. Likewise, the protein content of the bottom-scent vole did not affect the number of scent marks and over-marks deposited by the top-scent vole.