The interaction of tetramethylthiourea with a polycrystalline gold electrode in alkali and acid media has been studied. The behavior of the adsorbate was investigated by cyclic voltammetry, capacitance, and rotating disk measurements, and its orientation at the surface was determined by in-situ subtractively normalized interfacial Fourier transform infrared spectroscopy. In alkaline solutions tetramethylthiourea exhibits reversible potential dependent adsorption. Application of the IR metal-surface selection rule clearly shows that the molecule is adsorbed with the NC(S)N plane parallel to the surface. In acid solutions, tetramethylthiourea (TMTU) is adsorbed at the surface throughout the potential range investigated and at sufficiently positive potentials, dissolution of an Au(I)-TMTU complex into the thin layer between the electrode surface and the cell window was observed.