The electrochemical behavior of a PtRu(111) single crystal with 1:1 bulk atomic ratio is investigated for the first time by means of cyclic voltammetry and scanning tunneling microscopy (STM). The electrode surfaces are enriched with either Ru or Pt, depending on the cooling conditions after inductive heating. Analysis of the surfaces by STM shows a typical topography with smooth terraces separated by monoatomic high steps. The voltammetric characterization of PtRu(111) in acid media clearly reveals an altered electrochemical behavior of the Pt and Ru surfaces compared to Pt(111) and Ru(0001), respectively. Systematic changes are observed for hydrogen adsorption and underpotential deposition of copper as test reactions. Based on theoretical calculations in the literature, it is experimentally verified that the Pt-rich and the Ru-rich surfaces of the PtRu(111) single-crystal alloy bind adsorbates such as hydrogen significantly weaker and stronger than the pure single-crystal electrode surfaces. Such changes in surface reactivity can be crucial for electrocatalytic reactions.