The active principle of ARTEMISIA ANNUA L., artemisinin, is currently being developed to a registered antimalarial drug. For production purposes, plants with a high artemisinin content are required. We followed the development of the artemisinin content and of the biosynthetically related sesquiterpenes artemisinic acid, arteannuin B, and artemisitene in A. ANNUA plants, during a vegetation period in Vietnam, where this species is indigenous. In addition, the essential oil content and composition were studied. Samples of leaves, buds, flowers, or post-bloom flowers and fruits were taken at different stages: vegetative (5, 6, and 8 months old), at mass formation of buds (9 months), at full bloom (10 months), and post-bloom (10S months). The highest artemisinin content (0.86% dry wt) was present in the leaves of 5 months-old plants. At this stage also the highest leaf yield was found. Subsequently, the artemisinin content gradually dropped. At the age of 5 months the highest artemisinic acid and arteannuin B contents, 0.16 and 0.08% dry wt, respectively, were found as well. Artemisitene was present at all stages of development, ranging from 0.002 to 0.09% dry wt. With 1.9% v/w, the essential oil content was maximal just before flowering and was composed of 55% monoterpenes and 45% sesquiterpenes. At all other stages (0.4 - 1.0% v/w oil) this ratio was ca. 30%/70%. The main components of the oil were camphor and germacrene-D.

Artemisia annua L. (Asteraceae) contains artemisinin, a sesquiterpene lactone with promising antimalarial properties. At present the artemisinin content in plants grown in the open in the Netherlands is too low for industrial purposes. We describe a new method for laboratory selection to identify high yielding individual plants for the purpose of seed production and subsequent efficient cropping. During the procedure thin layer chromatography and high performance liquid chromatography were used as methods of analysis for artemisinin. Selected 11‐week‐old plantlets were transferred from the laboratory into the open in the summer of 1989. We have observed that plants which are high yielding in the laboratory continue to be so in the field. The A. annua crop which had been sown‐out directly had on average a 3–4‐fold lower artemisinin content.

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