The electrometric behaviour of homoconjugating systems containing protonated and free aliphatic amine N-oxide, i.e. trimethylamine N-oxide, in a number of non-aqueous solvents has been investigated by the use of a potentiometric titration method. The standard acidity constant K-a(o)(BH+) of protonated trimethylamine N-oxide and standard cationic homoconjugation constant K-f(o)(BHB+) in systems consisting of this free and protonated N-oxide were determined by e.m.f. measurements in a variety of polar non-aqueous solvents with diverse polarity and proton-donor properties, such as (aprotic, protophobic) acetone, acetonitrile, benzonitrile, nitromethane, propylene carbonate (aprotic, protophilic), N,N-dimethylformamide, and dimethyl sulfoxide, as well as (amphiprotic) methanol. It has been found that trimethylamine N-oxide has significantly higher basicity in non-aqueous media than substituted pyridine N-oxides (the pK(a)(o) value for protonated trimethylamine N-oxide being about 4 to 8.5 powers of 10 greater than those characteristic of pyridine N-oxide). Consequently, the tendency towards homoconjugation in trimethylamine N-oxide systems is also greater than for substituted pyridine N-oxide systems. Furthermore, the lower the basicity of a solvent, the higher the tendency of N-oxides towards homoconjugation.