Because electrophiles regulate many signalling pathways in cells, by modifying cysteine residues in proteins, they have a wide range of biological activity. In this study, a deuterium-labelling mass spectrometry-tandem diode-array detector (MS-DAD) screening method was established for rapid discovery of naturally occurring electrophiles. Glutathione (GSH) was used as a probe and incubated with natural product extracts. To distinguish different types of electrophile, incubation was performed in two reaction solvents, H(2)O and D(2)O. Ten types of naturally occurring electrophile were chosen, on the basis of their properties, to undergo the screening assay. By using this screening method, we successfully discovered the bioactive electrophile 4-hydroxyderricin in an ethanol extract of Angelica keiskei. This electrophile had potent NAD(P)H:quinone oxidoreductase 1 (NQO1)-inducing activity at a concentration of 20 μmol L(-1).