Methyl jasmonate is a sweet-smelling volatile compound often produced by plants in response to mechanical or biotic stress. Methyl jasmonate can stimulate synthesis of plant defense compounds including proteinase inhibitors and polyphenol oxidase. Exogenous application of methyl jasmonate as a gas or liquid can also induce plant defense responses against pests and/or pathogens. Artemisia tridentata produces copious amounts of methyl jasmonate that can induce defenses in nearby plants under laboratory and natural conditions. Therefore, it may be possible to use Artemisia as a source of methyl jasmonate for activating plant defenses in greenhouse production systems. For this reason, we are interested in understanding conditions that induce methyl jasmonate production in Artemisia spp. We examined the effect of irradiance and photoperiod on methyl jasmonate synthesis in three subspecies of Artemisia tridentata (tridentata, vaseyana, and wyomingensis) and two other Artemisia species (A. dracunculus and A. absinthium). A. tridentata contained 12-63 μg g-1 methyl jasmonate, which was greater than 10 times that found in A. dracunculus or A. absinthium. There was little difference in methyl jasmonate content among A. tridentata subspecies studied. Methyl jasmonate content increased as irradiance increased from 70 to 280 μmol m-2 s -1. Photoperiod had minimal effect on methyl jasmonate content in all species/subspecies studied.