Many textbooks point out that the thermodynamic stabilization enthalpy of 1 mol of 1,3-butadiene relative to 2 mol of 1-butene or to 1 mol of 1,4-pentadiene is slightly less than 4 kcal mol[superscript -1], owing to conjugation between the double bonds in the 1,3 configuration. It is reasonable to suppose that the analogous thermochemical stabilization enthalpy of 1,3-butadiyne would be somewhat greater than 4 kcal mol[superscript -1], perhaps as high as 7 or 8 kcal mol[superscript -1]. Thus it was with some surprise that we discovered, as subsequently verified by other groups, that the thermodynamic stabilization enthalpy of 1,3-butadiyne is zero. (Contains 1 table and 1 figure.)