The magnitude of the stabilizing interaction between an aliphatic C-H bond attached to an ammonium nitrogen and a carbonyl oxygen was evaluated by ab initio calculations at the MP2/6-311++G** level of theory. Attractive R3N+-C-H...O=C interactions play an important role in supramolecular recognition and various types of stereoselective catalysis. Our calculations show that R3N+-C-H...O=C is the strongest hydrogen bond of the C-H...O type known to date. Such hydrogen bonds remain as stabilizing interactions even in water for amide acceptors.