The relationship between environmental stress and the concentration of certain organic compounds (carbohydrates, tannins and phenolics) in plant leaves is examined. Pyrolysis-gas chromatography-mass spectrometry (PY-GC-MS) can be a rapid and comprehensive method to profile the chemical composition of biomaterials. Enhanced structural information on biomolecules containing acid functional groups can be obtained by a modification of direct pyrolysis; simultaneous pyrolysis methylation (SPM). Initial investigation focused on the characterization of important classes of biomarkers in leaves and optimization of sample preparation and pyrolysis conditions. The pyrolytic techniques were examined as a tool to quantify the compositional changes in leaves of trees which have been subjected to different environmental stresses. Results are reported for three field applications: the effect of thinning on balsam fir trees; the effects of fertilization on kalmia plant; and the effect of ozone on white pine trees. It was found that certain pyrolysates of carbohydrates, tannins and of a dihydrochalcone were good indicators of fertilization and water stress. Two unique pyrolysate biomarkers were discovered in white pine needles as indications of ozone fumigation levels and ozone damage. 132 refs., 33 figs., 13 tabs.