The essential oil obtained from the aerial parts of the Turkish endemism Siachys aleurites (Lamiaceae) has been studied. The main constituents were sesquiterpene hydrocarbons: beta-caryophyllene (33.7%), bicyclogermacrene (14.5%) and germacrene D (9.6%). The main monoterpene was alpha-pinene (8.4%). Some chernotax(o)nomical considerations have been provided. (C) 2004 Elsevier Ltd. All rights reserved.