Turnera ulmifolia L. is used in Brazilian folk medicine as an anti-inflammatory. Since this activity may be correlated with the presence of antioxidant compounds, a leaf extract was evaluated for its radical scavenging capacity (RSC). The in vitro RSC of a 50% hydroethanolic (HE) extract was evaluated by beta-carotene/linoleic acid coupled oxidation system for the inhibition of oxidation and the lipid peroxidation inhibition in rat brain homogenates, using thiobarbituric acid reactive substances (TBARS) and chemiluminescence (CL). Results indicated, through peroxidation suppression, that this extract exhibited greater antioxidative activity (77.4% +/- 10%) than alpha-tocopherol (58.4% +/- 3.7%). TBARS and CL inhibition was Concentration-dependent and Q(1/2) values were 8.2 and 6.0 mu g/mL for TBARS and CL, respectively. For alpha-tocopherol these values were 7.1 mu g/mL (TBARS) and 9.8 mu g/mL (CL). Phenolic compounds may be responsible for this antioxidant capacity. (c) 2005 Elsevier Ltd. All rights reserved.