This study was designed to examine the in vitro antioxidant activities of the methanol extracts of five Allium species, namely Allium nevsehirense, A. sivasicum, A. dictyoprosum, A. scrodoprosum subsp. rotundum and A. atroviolaceum; the former two are endemic for the Turkish flora. The extracts were screened for their possible antioxidant activities by two complementary tests; DPPH free radical-scavenging and beta-carotene/linoleic acid assays. In the first case, non-polar subfractions of the extracts did not show any antioxidant potential, while the polar subfractions exhibited marked activity. Among the polar ones, the most active one was A. atroviolaceum with an IC50 of 79.0 +/- 2.75 mu g/ml. In the beta-carotene/linoleic acid assay, the inhibition ratios of the oxidation of linoleic acid by A. atroviolaceum and A. dictyoprosum were too close to each other (71.2 +/- 2.20% and 72.3 +/- 1.20%, respectively), while that of the synthetic antioxidant, BHT, was 96%. (c) 2004 Elsevier Ltd. All rights reserved.