To contribute to the understanding of the mechanisms underlying the beneficial effects of licorice, the antioxidant, free radical-scavenging and immunostimulating effects of a licorice infusion (LI) were investigated, and its chemical profile was determined. Two major components of LI were identified as (1) liquiritin and (2) glycyrrhizin. LI weakly scavenged DPPH{radical dot}, and compounds 1 and 2 showed negligible effects. Both LI and 2 substantially scavenged superoxide radicals. The β-carotene bleaching was inhibited by LI, but compounds 1 and 2 showed no effect. The LI, 1, and 2 exhibited no meaningful activities against HOCl, and they showed pro-oxidant effects in the MPO-chlorinating system. Granulocytes and NK cells were markedly activated by LI, whereas 1 and 2 were inactive. The LI, 1, and 2 showed no effects on the lymphocyte cell cycle. These results support, in part, the traditional use of licorice to treat and prevent diseases in which oxidants or free radicals are implicated and suggest that LI could be used as a potential non-specific immune stimulator. © 2010 Elsevier Ltd. All rights reserved.