The terpenoids constitute the largest class of natural products and many interesting products are extensively applied in the industrial sector as flavors, fragrances, spices and are also used in perfumery and cosmetics. By their nature, plants protect themselves by producing some compounds called as secondary metabolites, including terpenes. Significance of constitutive and induced terpenoid defences in conifer resistance is briefly presented. Better knowledge of the mechanism of action of individual terpanes and about the additive and synergistic effects of compounds, will have important implications for forest and agricultural management of pests and pathogens Terpenoids represent the largest and most diverse class of chemicals among the myriad compounds.
