The quaternary ammonium groups of suxamethonium have been replaced by amidinium, guanidinium and thiouronium groups. The guanidine compound exhibited competitive neuromuscular activity of a low order of potency; the other compounds were ineffective. Replacement of the quaternary ammonium groups in decamethonium by ethylmethylsulphonium or dimethylsulphoxonium groups gave less potent, depolarizing agents.