The bactericidal activity of mixtures of higher aliphatic quaternary ammonium salts containing varying proportions of the saturated and unsaturated C18 chain does not vary markedly with degree of unsaturation. There is however, a significant tendency toward higher activity in the mixtures of lower degrees of unsaturation. In the series of compounds studied, no individual can be classified as most active against all organisms. In general, the hexadecyl and the tallow derivatives are superior. On the basis of commercial availability of the raw material, and the antimicrobial activity and physical properties (solubility and crystallinity) of the product, it is concluded that among the compounds studied the trimethylalkylammonium chloride derived from tallow fatty acids is the most suitable salt for commercial development.