AbstractThe content and chemical composition of essential oil of leaves, inflorescences and rhizomes of Silphium perfoliatum L. were studied in this paper. The mean content of oil in leaves amounted to 0.19% v/w per dry matter; inflorescences contained 0.27% v/w of oil per dry matter, while the rhizomes contained 0.41% v/w. Qualitative and quantitative analysis of distilled oils were carried out using the GC and GC–MS technique. The chemical composition of the essential oils obtained from inflorescences and leaves is quite similar, although in the inflorescence oil the dominant constituent is the bicyclic monoterpene α‐pinene (16.0–20.9%), and in the leaf oil the prevailing components are the bicyclic sesquiterpene caryophyllene oxide (8.5–34.7%) and the monocyclic sesquiterpene germacrene D (6.4–24.3%). In the rhizome oil from Silphium perfoliatum L., the dominating compounds are the tricyclic sesquiterpenes 7‐β‐H‐silphiperfol‐5‐ene (5.7–14.9%), isocomene (2.8–14.4%), modhephene (2.3–9.9%), 7‐a‐H‐silphiperfol‐5‐ene (1.2–9.7%), which considerably differentiates this oil from those obtained from the leaves and inflorescences. Copyright © 2004 John Wiley & Sons, Ltd.