Essential oil was extracted from yarrow flowers (Achillea millefolium) with supercritical CO2 at pressure of 10 MPa and temperatures of 40-60 degrees C, and its composition and yield were compared with those of hydrodistillate. The yield of total extract, measured in dependence on extraction time, was affected by extraction temperature but not by particle size of ground flowers. CO2-extraction of cuticular waxes was lowest at 60 degrees C. Major essential oil components were camphor (26.4% in extract, 38.4% in distillate), 1,8-cineole (9.6% in extract, 16.2% in distillate), bornyl acetate (16.7% in extract, 4.3% in distillate), gamma-terpinene (9.0% in extract, 9.4% in distillate), and terpinolene (7.6% in extract, 3.9% in distillate). Compared to hydrodistillation, the yield of monoterpenes was lower due to their incomplete separation from gaseous CO2 in trap but the yield of less volatile components like monoterpene acetates and sesquiterpenes was higher. Hydrolysis of gamma-terpinene and terpinolene, occuring in hydrodistillation, was suppressed in supercritical extraction, particularly at extraction temperature of 40 degrees C. (c) 2006 Elsevier B.V. All rights reserved.