The effect of adsorption of triphenylphosphine, -arsine, -stibine and -bismuth on Hg from methanolic solution on electrode reactions was studied by a polarographic technique. In view of the fact there are no data on the interfacial behaviour of triphenylbismuth, its absorption on a mercury electrode was first studied by means of electrocapillary measurements. The results show that the interfacial behaviour of triphenylbismuth is analogues to that of the other three compounds. The catalytic behaviour of these substances on the hydrogen evolution on Hg and their inhibitory action on the reduction of o-dinitrobenzene, oxygen and the cations Cd 2+ and Zn 2+ were also investigated. Results suggest that triphenylbismuth, and to a lesser degree triphenyl phosphine, exhibit the stronger, and triphenylarsine and -stibine the weaker, catalytic action. The inhibitory action can be due either to the reduction of the interfacial concentration of H + as in the case of o-dinitrobenzene or to the blocking of the electrode surface as in the case of the reduction of oxygen, Cd 2+ and Zn 2+. The extent of the inhibitory action is analogous to the surface coverage of the electrode surface by the additive molecules.