The application of pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) to the analysis of natural resins and resinites based on diterpenoid carboxylic acids has been investigated, in order to determine the usefulness of this technique for the analysis of these materials. It has been found that Py-GC/MS analyses using simultaneous pyrolitic methylation (SPM) provide an accurate indication of the composition of these materials, except with respect to compounds with an additional hydroxyl and/or carbonyl functionality. Resin acid methyl esters (RAMES) are efficiently produced in situ by copyrolysis with tetramethylammonium hydroxide. Pyrolysis did not result in significant thermal degradation or isomerization of the RAMES characterized in this study. Some dehydration of RAME alcohols is observed however, and both hydroxyl- and carbonyl-containing RAMES undergo undesirable side reactions with the methylating reagent, which results in the formation of nitrogen-containing products. The optimum pyrolysis temperature for low- to moderate-rank resinites using the conditions employed in this study was found to be 480[degree]C. Py-GC/MS analyses without in situ methylation were found to provide generally less adequate data for structural and compositional analyses.