Summary.The pharmacological properties of trimethyl‐, dimethylethyl‐, methyldiethyl‐ and triethyl‐phenylammonium have been investigated.The toxicity of the substances in mice and rabbits was determined. The cause of death in all the cases appeared to be peripheral paralysis of respiration.Trimethyl‐, dimethylethyl‐ and methyldiethyl‐phenylammo‐nium had a parasympathicomimetie effect on the blood‐pressure. The parasympathicomimetic activity diminished as the number of ethyl radicals increased.Triethylphenylammonium decreased the blood‐pressure. This effect was not reversed by atropin.Trimethyl‐, dimethylethyl‐ and methyldiethyl‐phenylammo‐nium had a “nicotinic‐stimulating” action. This effect too diminished according as the number of ethyl radicals increased. Triethylphenylammonium had no “nicotinic‐stimulating” action.All the substances had a paralyzing effect on the sympathetic ganglion. It was most marked in dimethyl‐ and triethylphenylammonium and least in trimethylphenylammonium.All the substances examined have shown, in muscle‐nerve preparations, a curariform effect. The effect was strongest in the trimethyl compound and diminished according as the number of ethylradicals increased.The effect of these substances on the isolated rabbit heart have been tested.The syntheses of trimethyl‐, dimethylethyl‐, methyldiethyl‐ and tr