The phytotoxicity of the three major monoterpene constituents of the essential oil from leaves of Artemisia scoparia Waldst. & Kit. (redstem wormwood) was investigated. GC/GC-MS analysis revealed that the essential oil (yield 0.84%) is a complex mixture containing 19 monoterpenes, 7 sesquiterpenes and 15 other compounds--aliphatic alcohols, ketones, aromatic hydrocarbons and esters. The three major monoterpenes were beta-myrcene (30.2%), p-cymene (12.8%) and dl-limonene (12.4%). The essential oil and the three monoterpenes exhibited phytotoxicity and reduced germination, seedling growth, chlorophyll content and percent respiration of Avena sativa and Triticum aestivum in a dose-response manner. The inhibitory effect of monoterpenes was comparatively smaller than of the crude essential oil and beta-myrcene was most toxic followed by p-cymene, whereas limonene was least toxic. The study suggests that A. scoparia oil and beta-myrcene can be explored for phytotoxicity against weeds.