Specimens of ultra high strength steel were charged cathodically with hydrogen or immersed without charging in a normalNaOH solution of NaC14N and the adsorption of C14N groups determined by means of radioactivity measurements. In addition, the desorption of adsorbed C14N groups was also studied. Heats, designated heats of adsorption, energies of activation, and the surface coverage with C14N were calculated. Hydrogen embrittlement by measurement of bend ductility, negative overvoltage, and the relative hydrogen coverage were determined under similar conditions and with similar materials. It is concluded that C14N groups are strongly and preferentially adsorbed on highly active centers and the hydrogen recombination reaction retarded accordingly. The rapid increase in hydrogen embrittlement with increasing surface coverage by C14N is ascribed to a high surface concentration of the embrittling hydrogen atoms, followed by rapid migration into the steel.