A pyrolysis derivatisation technique involving co-pyrolysis with tetramethylammonium hydroxide was used to chemically characterise heartwood lignocellulose from selected softwoods and hardwoods, including a number of Eucalyptus hardwood species. The process is considered to be a thermally-assisted hydrolysis and methylation reaction, previously termed simultaneous pyrolysis methylation. The composition of lignin-derived guaicyl and syringyl dimethoxy- and trimethoxybenzenoid compounds could be used to distinguish softwoods from hardwoods and, in particular, gymnosperms from angiosperms. The relative proportion of the products was used to differentiate between the woods in this study. A case study to distinguish two species of cypress by the technique is presented. Compounds not usually associated with lignocellulose were identified as extractives, the subject of the second part of this study. Heartwood and sapwood components were studied.