Isomeric C6H6 species produced by high-pressure shock tube pyrolysis of 1,5-hexadiyne have been investigated by gas chromatography-matrix isolation FTIR spectroscopy-mass spectrometry. In addition to benzene (stable end product) and 1,5-hexadiyne (starting material), six isomeric C6H6 species have been identified on the basis of spectroscopic characteristics. The results are consistent with theoretical predictions of stable species that will be formed in the pyrolysis of 1,5-hexadiyne and key species have been positively identified for the first time.