Artemisinin content in hairy roots of Artemisia annua was increased from 0.8 mg g(-1) dry wt to 1 mg g(-1) dry wt by using elicitor treatment of mycelial extracts from the endophytic fungus Colletotrichum sp. The increase of artemisinin was dependent on the growth stage of hairy roots as well as on the dose of the elicitor applied. When hairy roots of 23-day-old cultures (later growth phase) were exposed to the elicitor at 0.4 mg total sugar ml(-1) for 4 days, the maximum production of artemisinin reached to 13 mg l(-1), a 44% increase over the control. This is the first report on the stimulation of artemisinin production in hairy roots by the elicitor from an endophytic fungus of A. annua.