The herb, Artemisia annua L., a member of the Compositae family, has been used for many centuries in Chinese folk medicine to alleviate the chills and fever of malaria. In 1967, a search for new antimalarial drugs from traditional remedies was initiated in China; early extractions with hot H₂O or EtOH failed to confirm efficacy, but later Et₂O extraction yielded a neutral fraction active against Plasmodium berghei (mice) and P. cynomolgi (monkeys). In 1972, the active crystalline constituent was isolated from aerial parts (0.01-0.5% yield), and its structure was reported in 1979 as artemisinin (qinghaosu), a sesquiterpene lactone with a peroxide function (destruction eliminates antimalarial activity). It has cured over 2000 patients with P. vivax and P. falciparum, including chloroquine-resistant P. falciparum and cerebral malaria; derivatives with higher potency exist, and its synthesis has been described. Confusion exists over the Chinese name of A. annua (e.g., qinghao, hang hua hao). To determine if U.S.-grown A. annua contains artemisinin, the authors collected the weed, air-dried it, and extracted with petroleum ether (30-60℃, most selective). From 200 g air-dried leaves (August 1983), 0.12 g (0.06% yield) of fine white crystals (mp 153-154℃) was obtained, confirmed as artemisinin via comparative mp, superimposable IR, identical NMR/[α]D, and MS (m/z 283, C₁₅H₂₂O₅). Ten other U.S. Artemisia species lacked artemisinin. In vitro, artemisinin was potent against chloroquine-susceptible and -resistant P. falciparum (mean IC₅₀ <3.4 ng/ml, comparable to mefloquine) but had no antibacterial activity against Gram-positive (e.g., Staphylococcus aureus, Streptococcus faecalis) or Gram-negative organisms (e.g., Escherichia coli, Neisseria gonorrhoeae), with MIC >32 μg/ml or >1 μg/ml.