Elevated levels of monoterpenes and diterpene resin acids are produced in the stems of lodgepole pine (Pinus contorta var latifolia) saplings when wounded and inoculated with the blue-stain fungus Ceratocystis clavigera or when wounded and treated with a pectic fragment from tomato leaves (PIIF) or a fungal cell wall fragment (chitosan). This induced defensive response (hyperoleoresinosis) is the result of a transient rise in the ability to biosynthesize cyclic monoterpenes and diterpene resin acids as measured by the in vivo incorporation of label from [U-(14)C]sucrose relative to untreated controls, and is accompanied by a corresponding rise in the levels or activities of the relevant terpene cyclases as determined by in vitro assay using labeled acyclic precursors. The results indicate that juvenile P. contorta responds to infection and biotic elicitors much like the mature tree, and they suggest that the Pinaceae possess a mechanism for elicitor recognition and induced defense similar to that of other higher plants.