The adsorption of isomeric butanediols at the free surface of the aqueous solution has been studied by measuring the surface pressure and the adsorption potential shift. Surface excesses, determined from the Gibbs equation, have been worked out by testing three adsorption isotherms. The adsorption patterns indicate that isomers whose molecules can provide intramolecular hydrogen bonds behave differently from those only providing intermolecular interactions. In particular, the former isomer group exhibits somewhat more hydrophobic features. Adsorption at the free surface of the solution has been compared with that at the Hgsolution interface for butane-1,4-diol only. A higher surface activity at the Hg electrode has been interpreted in terms of the prevalence of metal-adsorbate interactions via the functional groups. The surface potential of the pure solvents has also been measured with respect to water and compared with calculations based on the "macroscopic model" recently proposed by the present authors.