The dienophile 4-methyl-1,2,4-triazoline-3,5-dione (MTAD) adducts of conjugated diene compounds were used to locate the position of the conjugated double bonds in the parent compounds by high-resolution gas chromatography and electron impact mass spectrometry. Their mass spectra are marked by recognizable molecular ions and abundant diagnostic ions that allow the determination of the diene position. With the identification of the sex pheromone gland extracts of Yunnan pine caterpillar moth Dendrolimus houi as an example, the characteristics of reaction of (E, Z)-5,7-dodecadien-1-ol (E5, Z7-12: OH) and its corresponding aldehyde and acetate with MTAD are discussed. Potential problems in gas chromatographic analysis are also discussed.