Stress-induced changes in the emissions of volatiles from many economically-important plants have been demonstrated in studies over the past decade. Plants such as cotton and corn change both the composition and concentration of their emissions when subjected to wounding, herbivory and pathogen attack. Terpene-accumulating plants have been overlooked as potential objects of such studies although work on conifers has shown that species rich in constitutive defences can also exhibit induced responses. The aim of this study was to investigate whether terpene-accumulating plants respond to stress by altering their foliar emissions qualitatively and/or quantitatively. Species examined included Salvia officinalis (common sage), Melaleuca alternifolia (Australian tea tree) and Ocimum minimum (Bush basil). An experimental design was developed to eliminate factors such as leaf ontogeny that can affect the obtained results and complicate their interpretation. Small-scale solvent extraction and HS-SPME-based techniques were also developed; they enabled the quantitative determination of treatment-induced changes over periods ranging from 10 minutes to 6 months. Treatment of plants included mechanical wounding, herbivory, pathogen attack and chemical elicitation. Overall, statistically significant induced-changes were observed for both leaf-oil composition and concentration. The response of the different species used varied. O. minimum exhibited the greatest compositional changes whilst M. alternifolia was the only species for which oil-concentration changes were observed. The demonstrated changes were not as great as those reported in similar studies with non-terpene producing plants. The results indicate that the high metabolic costs associated with the production and storage of constitutive defences may be responsible for the limited induction of further defensive responses / Doctor of Philosophy (PhD)