This study was designed to determine the antioxidant potentials of various extracts and the essential oil obtained from the leaves of Hyssopus officinalis L. ssp. angustifolius (Lamiaceae). The hexane, chloroform and water extracts were prepared by using an automated extraction system while essential oil was obtained from water-distilation by using Clevenger-type apparatus. Methanol-water (1:1) extract was also prepared by maceration. All extracts were evaluated for their abilities to scavenge free radicals (DPPH method) and inhibition of the oxidation of linoleic acid (beta-caroten/linoleic acid) in vitro test systems. In DPPH test, water extract exhibited higher radical scavenging activity. The 50% inhibition (IC50) values of the water, methanol-water and chloroform extracts were 18.80, 28.80 and 250 mu g ml(-1), respectively. On the other hand, the non-polar extracts were active in beta-carotene/linoleic acid test system. The essential oil did not exert activity in both tests. Both total phenolics and total flavonoid contents were highest in the water extract possessing 4.70% (as gallic acid equivalent) and 1.30%, respectively. Proantho-cyanidine was confirmed to be present at high concentrations in all samples, particularly in chloroform extracts (10,250 mg/L). HPLC analysis of methanol extracts showed the presence of antioxidant phenolic compounds such as chlorogenic acid (166.21 gg(-1)) and caffeic acid (111.09 gg(-1)), both were the major phenolics. Automated extraction system provided better separation of the active principles than conventional standard extraction procedures. (C) 2012 Elsevier B.V. All rights reserved.