The effect of an extract of Dalbergiae Lignum and four components that were isolated from the extract on the anticarcinogenic phase II marker enzyme, quinone reductase (QR), was investigated. Of the solvent extracts of Dalbergiae Lignum, the CH2Cl2 fraction was the most potent in inducing QR activity, with a CD value (the concentration required to double the QR activity) of 29.5 microg/mL. The CH2Cl2 extract was further separated into six compounds, four of which were identified as 4-methoxydalbergione, latifolin, 4',6-dihydroxy-7-methoxyflavanone, and obtusafuran. Obtusafuran [CD = 1.1 microM; chemopreventive index (CI) = 101.9] and latifolin (CD = 1.7 microM; CI = 154.6) displayed potent QR inducing activity and high chemopreventive indices. Latifolin and 4-methoxydalbergione were identified as strong DPPH-scavengers with half-maximal free radical scavenging concentrations of 15.9 and 17.2 microM, respectively.