Monolayers of 2- and 4-heptadecylpyridine 1-oxide have been studied as analogues of the poly(vinylpyridine oxides). Differences between the π–A curves are explained in terms of the orientation of the molecules. Unlike ethylpyridine oxides, which do not form monolayers, both heptadecylpyridine oxides interact with monosilicic acid to give solid films.