Enthalpies of combustion and sublimation have been measured for 1,3,5-triazine. Enthalpies of formation in the solid and gaseous states have been derived: ΔH f o(cr) = (171.69±0.77) kJ · mol −1 and ΔH f o(g) = (225.87±0.89) kJ · mol −1. The conventional stabilization energies of six-membered aromatic rings containing one, two, or three nitrogens are discussed. The use of more up-to-date bond-energy terms gives results quite different from those previously reported. For instance, no regular decrease in stabilization energy upon substitution of CH by N is observed. Also, the stabilization energy of pyridazine (1,2-diazine) turns out to be significantly lower than those of the 1.3- and 1.4-diazines.