The in vitro antimicrobial and antioxidant activities of the essential oil and methanol extracts of Achillea millefolium subsp. millefollium Afan. (Asteraceae) were investigated. GC-MS analysis of the essential oil resulted in the identification of 36 compounds constituting 90.8% of the total oil. Eucalyptol. camphor, alpha-terpineol, beta-pinene, and borneol were the principal components comprising 60.7% of the oil. The oil strongly reduced the diphenylpicrylhydrazyl radical (IC50 = 1.56 mug/ml) and exhibited hydroxyl radical scavenging effect in the Fe3+-EDTA-H2O2 deoxyribose system (IC50 = 2.7 mug/ml). It also inhibited the nonenzymatic lipid peroxidation of rat liver homogenate (IC50 = 13.5 mug/ml). The polar phase of the extract showed antioxidant activity. The oil showed antimicrobial activity against Streptococcus pneumoniae, Clostridium perfringens, Candida albicans, Mycobacterium smegmatis, Acinetobacter lwoffii and Candida krusei while water-insoluble parts of the methanolic extracts exhibited slight or no activity. This study confirms that the essential oil of Achillea millefolium possesses antioxidant and antimicrobial properties in vitro. (C) 2003 Elsevier Science Ireland Ltd. All rights reserved.