The aim of the present study was to investigate the protective effects of infusions prepared from 15 Achillea (Asteraceae) species against H2O2-induced oxidative damage in human erythrocytes and leucocytes used in traditional Turkish medicine. CAT, SOD and GPx activities, effects of LPO and GSH levels of the infusions on erythrocytes and leucocytes were assessed. The results indicated that all infusions of Achillea species were effective on antioxidant enzyme systems of erythrocytes and leucocytes when compared with H2O2 group. Achillea falcata was the most effective one on CAT, GPx and SOD enzyme systems of erythrocytes. Among plant infusions, Achillea crithmifolia and Achillea nobilis subsp. neilrechii showed the highest activities on CAT, while Achillea millefolium subsp. pannonica on SOD, Achillea teretifolia on GPx and Achillea nobilis subsp. sipylea on LPO enzyme systems of leucocytes. The present results demonstrate that infusions of Achillea species are a potential source of natural antioxidants for treatment and prevention of diseases in which LPO takes place. (c) 2005 Elsevier Ireland Ltd. All rights reserved.