Quaternary ammonium salts of the formula <FORM:0648400/IV (b)/1> where R1 is an alkyl group with 12 to 18 carbon atoms, R2 is benzyl and X is the anion of naphthenic acid, are obtained by treating water-soluble salts of the same cation with naphthenic acid in the presence of an alkali, or by treating the quaternary hydroxide with naphthenic acid. Examples are given where R1 is n-dodecyl, cetyl or derived from the mixture of amines obtained from coconut fatty acids. In the Specification as open to inspection under Sect. 91 the production is referred to of quaternary salts NR1R2R3R4X where R1-R4 are aliphatic, alicyclic, aromatic or heterocyclic radicals which may be substituted, and two or three of them may represent a closed ring; X is the anion of a water-insoluble oil-soluble acid. Apart from the radicals specified above, the following are mentioned: 9-octadecenyl, ethyl and propyl, and X may be oleate, tallate, 2-ethyl-hexoate, linoleate, laurate, mono-octyl phthalate, p-tert.-amylphenoxy-acetate and "alkyl sulphonate" (derived from sulphonated mineral oils). Laurylpyridinium is also specified as a cation, and the following salts are mentioned: dodecyl - dimethyl - o - chlorbenzyl - ammonium lineolate, di - isobutyl-phenoxyethoxyethyl - dimethyl - benzyl ammonium 2 - ethyl - hexoate, p - tert. - octylphenoxyethoxyethyl - dimethyl - benzylammonium oleate and N-(lauric acid ester of colamino - formyl - methyl) - dimethyl - benzylammonium naphthenate. Double salts may be formed, e.g. laurylpyridinium naphthenate +2 - ethyl - hexoate and laurylpyridinium +dodecyl - dimethyl - benzyl - ammonium naphthenate. These salts may be prepared by either of the processes mentioned above. This subject-matter does not appear in the Specification as accepted.ALSO:Quaternary ammonium salts of the formula <FORM:0648400/VI/1> where R1 is an alkyl group with 12 to 18 carbon atoms, R2 is benzyl and X is the anion of naphthenic acid are used as pest-control agents in various ways:-(1) in marine anti-fouling paints to counteract the activities of marine organisms; (2) applied to economic crops as aqueous emulsions which may be diluted with an inert carrier such as bentonite; (3) to prevent bacterial attack by incorporation in casein- and oil-paints, varnishes, plastic- and other film-forming agents, polishes and waxes. The compounds may be dissolved in hydrocarbon or vegetable oils with or without another solvent such as ethyl alcohol or ethylene glycol monoethyl ether. Other fungicides such as metallic naphthenates, oleates and tallates may be added. In specified compounds, the group R1 is cetyl, dodecyl and the alkyl groups derived from the acids in coconut oil. The Specification as open to inspection under Sect. 91 refers to quaternary salts NR1 R2 R3 R4 X where R1-R4 are aliphatic, alicyclic, aromatic or heterocylic radicals which may be substituted, and two or three of them may represent a closed ring; X is the anion of a water-insoluble oil-soluble acid. The following naphthenates are specified:-lauryl - pyridinium, 9 - octa - decenyl-dimethyl-ethyl-ammonium, tetraethylammonium and dimethyl-ethyl-propyl ammonium, and also the oleates, tallates (from tall oil), 2-ethyl-hexoates and alkyl-sulphonates (from sulphonated mineral oil) of lauryl-pyridinium, "alkyl"-dimethyl-benzyl-ammonium (from coconut oil as above), cetyl-dimethyl-benzyl-ammonium and 9-octadecenyl-dimethyl-ethyl-ammonium; and in addition "alkyl"-dimethyl-benzyl-ammonium laurate and linoleate. The following compositions contain two active ingredients:-lauryl-pyridinium naphthenate + lauryl-pyridinium 2-ethyl-hexoate, lauryl-pyridinium naphthenate + dodecyl-dimethyl-benzyl-ammonium naphthenate, lauryl-pyridinium naphthenate + copper naphthenate, "alkyl"-dimethyl-benzyl ammonium naphthenate + copper oleate, 9-octadecenyl-dimethyl-ethyl-ammonium tallate + zinc 2-ethyl-hexoate, "alkyl"-dimethyl-benzyl-ammonium naphthenate + a phenol-formaldehyde resin, "alkyl"-dimethyl-benzyl-ammonium linoleate or naphthenate + zinc naphthenate. Additional compounds mentioned are:-didodecyl-dimethyl-ammonium naphthenate, dodecyl-dimethyl-benzyl-ammonium laurate and mono-octyl phthalate, dodecyl-dimethyl-o-chlorbenzyl-ammonium linoleate, di-isobutylphenoxy-ethoxyethyl-dimethyl-benzyl-ammonium 2-ethyl-hexoate, lauryl-pyridinium p-tert.-amylphenoxyacetate, p-tert.-octylphenoxy-ethoxyethyl-dimethyl-benzyl - ammonium oleate and N-(lauric acid ester of colaminoformyl methyl)-dimethyl-benzyl-ammonium naphthenate. This subject-matter does not appear in the Specification as accepted.