The enthalpy of formation of HNC is determined using collision-induced dissociation threshold measurements with protonated nitriles. The average value obtained using five different nitrile precursors is 49.7 +/- 2.9 kcal/ mel, which agrees with the previously reported experimental value after accounting fur revisions in the proton affinity scale. While the main dissociation pathway for all ions is found to be simple cleavage, the protonated propionitrile and acrylonitrile ions also dissociate by formation of HCNH+ formed by intramolecular proton transfer.