This study was designed to examine the in vitro antioxidant activities and rosmarinic acid levels of the methanol extracts of Salvia verticillata subsp. verticillata and S. verticillata subsp. amasiaca. The extracts were screened for their possible antioxidant activity by two complementary test systems, namely DPPH free radical-scavenging and beta-carotene/linoleic acid systems. In the first case, S. verticillata subsp. verticillata was superior to the subsp. amasiaca with an IC50 value of 14.5 +/- 1.21 mu g mg(-1). In the beta-carotene/linoleic acid test system, inhibition capacity of S. verticillata subsp. verticillata was 74.4 +/- 1.29%. Antioxidant activities of BHT, ascorbic acid, curcumin and alpha-tocopherol were determined in parallel experiments. Activity of rosmarinic acid was also screened for better establishing the relationship between rosmarinic acid level and antioxidant activity for the plant extracts. S verticillata subsp. verticillata had the highest rosmarinic acid level with a value of 28.7 +/- 0.89 mu g mg(-1). There is a strong correlation between the rosmarinic acid level and antioxidant activity potential. Our results showed that rosmarinic acid and its derivatives are more likely to be responsible for most of the observed antioxidant activities of Salvia species. (c) 2005 Elsevier Ltd. All rights reserved.