DDT nearly eradicated mosquitoes, carriers of Plasmodium species, the cause of malaria in humans. However, the ecological and other problems arising from this chemical eventually limited its use, and the mosquito and malaria have returned with a vengeance. Artemisinin is an anti-malarial drug, derived from the ancient Chinese remedy qinghao, isolated from a common weed. This remarkable compound is the only 1,2,4-trioxane found in Nature and will aid the chemotherapy of malaria, which hitherto has relied on quinine and its synthetic analogues.