[en] Transformed cultures of Artemisia annua L. (Asteraceae) were established by the co-culture method using leaf segments of A. annua and Agrobacterium rhizogenes NCIB 8196 or MAFF 03-01724. The hairy root clones thus obtained grew vigorously on hormone-free medium, showing the typical transformed morphology. The genetic transformation of the root was proved by the opine assay. Normal root and shoot cultures were also established. A highly specific and sensitive enzyme-linked immuno-sorbent assay (ELISA) method was used for the detection and semi-quantitative determination of artemisinin and structurally related compounds in these cultures. The presence of artemisinin was confirmed by gas chromatography coupled to mass spectrometry (GC-MS) analysis. The hairy roots cultured in the dark produced no detectable level of artemisinin as shown by the adventitious shoots cultured under light conditions. The ELISA analysis of the green hairy roots cultured in liquid medium under a 16 h light/day photoperiod showed the existence of compound(s) structurally related to artemisinin, though normal and hairy roots cultured in the dark give no detectable levels of immuno-signal.