The presence of intramolecular hydrogen bonding in 2-nitro-1-naphthylamine, 1-nitro-2-naphthylamine, 3-nitro-2-naphthylamine, and 8-nitro-1-naphthylamine is inferred from a study of the NH frequencies of the 14 isomeric mononitronaphthylamines in the solvents carbon tetrachloride and pyridine. The NH stretching frequencies are decreased in pyridine as a result of hydrogen bonding between the amino group and the solvent. The extent of this decrease is quite uniform for all nitronaphthylamines except those in which the nitro and amino groups are adjacent, and in these cases the decrease is about half that observed from the remaining compounds. This is interpreted as indicating the presence of intramolecular hydrogen bonding in the latter group, the extent of which reduces the degree of solvent-solute interaction.