The methanolic extracts of several natural medicines and medicinal foodstuffs were found to show an inhibitory effect on rat lens aldose reductase. In most cases, flavonoids were isolated as the active constituents by bioassay-guided separation, and among them, quercitrin (IC 50= 0.15 μM), guaijaverin (0.18 μM), and desmanthin-1 (0.082 μM) exhibited potent inhibitory activity. Desmanthin-1 showed the most potent activity, which was ...