1. A study of the adsorption of cyclohexane vapor on the walls of a capillary made of an alloy of palladium with 6% ruthenium showed that in the presence of hydrogen the adsorption of cyclohexane was intensified if the alloy was in the state of the hydrogen-poor α phase. At higher partial pressures of hydrogen, when the alloy consisted of the β phase, the adsorption of cyclohexane vapor decreased with increasing partial pressure of hydrogen in the mixture. In all cases, the cyclohexane adsorption isotherms were linear. 2. The obtained results were explained on the basis of the concept that on the α-phase surface the hydrogen was predominantly in the atomic state and attracted oppositely polarized molecules of the adsorbed cyclohexane, while the surface of the β phase was occupied mainly by hydrogen molecules, with which the cyclohexane molecules entered into adsorption competition. © 1983 Plenum Publishing Corporation.