Brain cellular functions are affected by free radicals. Arachidonic acid and its 12-lipoxygenase metabolites have been proposed as important in enhancing long-term potentiation associated with learning. It has been reported that Student Rasayana (SR), an herbal mixture, improves brain functions. In this study we evaluated the antioxidant capacity of SR and its effect on lipoxygenase activity. Both alcoholic and aqueous extracts of SR inhibited enzymatic- and nonenzymatic-induced microsomal lipid peroxidation in a concentration-dependent manner. The agent concentrations (micrograms/mL) that produced 50% inhibition (IC50) of enzymatic- and nonenzymatic-induced microsomal lipid peroxidation, respectively, were 99.1 +/- 3.9 and 1992.0 +/- 122.7 for the aqueous extract, and 17.7 +/- 0.9 and 646.7 +/- 79.7 for the alcoholic extract. The aqueous extract inhibited soyabean lipoxygenase (SLP)-induced LDL oxidation in a concentration-dependent manner (IC50: 515.5 +/- 11.5), whereas the alcoholic extract enhanced SLP-induced LDL oxidation. Simultaneous addition of aqueous and alcoholic extracts inhibited SLP-induced LDL oxidation. The alcoholic extract (but not the aqueous extract) enhanced the ability of SLP to induce oxidation of linoleic acid. Rats fed 2% (w:w) SR showed inhibition of toluene-induced brain microsomal lipid peroxidation. These results suggest SR improves brain functions through scavenging free radicals as well as increasing the second messenger for long-term potentiation.