In the course of mechanistic studies on HCN+ isomerization in reaction with CO and CO2, we have fortuitously determined the heats of formation of HNC and HNC+ with good precision. The uncertainty is the uncertainty in the heat of formation of HCN, +/- 1 kcal mol(-1). This appears to be the first precise experimental determination of these energies. Several prior theoretical calculations have produced reasonable energy values. We also observed the reaction of HCN+ with CF4 to be slightly endothermic, which allows the determination of an upper limit on the threshold energy for CF4 --> CF3+ + F of 14.28 eV, in excellent agreement with several prior determinations but in sharp disagreement with the most recent determination.