GC-MS analysis of the isolated essential oils from air-dried aerial parts of Achillea setacea and Achillea teretifolia, an endemic taxon, resulted in the identification of 51 constituents (79.8% of the total oil) and 42 constituents (87.1% of the total oil), respectively. Eucalyptol (1,8-cineole) was the major constituent of both oils studied (18.5 and 19.9%, respectively). The antimicrobial activities of the essential oils were individually evaluated against 14 microorganisms. Both oils exhibited inhibitory effects on Clostridium perfringens, Acinetobacter Iwoffii and Candida albicans with a range of minimum inhibitory concentration values extended from 0.28 to 2.25 mg/ml. Camphor and their derivatives, borneol, terpinen-4-ol and eucalyptol (1,8-cineol) can be considered as the main antimicrobial constituents of the oils studied. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.