The volatile fraction ofT. partheniumis characterized by a high camphor (44%) and trans-chrysanthenyl acetate (23%) content.T. vulgareoils, obtained from specimens growing in the province of Eastern Flanders (Belgium), conformed to the infra-specific chemical variability; three chemical types were identified: i.e., the β-thujone, trans-chrysanthenyl acetate and camphor/β-thujone types. A small scale experiment confirmed the mosquito-repellent activity ofT. vulgare, without allowing the identification of the active principle. However, the activity was much lower than that of diethyltoluamide containing commercial preparation.