Registered by the World Health Organization (WHO), 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) is one of the strongest bacterial mutagens ever tested, as highlighted by the Ames Salmonella typhimurium TA100 assay. We provide new insights concerning this mutagenic activity on the basis of global and local theoretically defined electrophilicity indices. Our results further support the idea that mutagenicity of MX and its analogues is related more closely to one-electron transfer processes from the electron-rich biological environment than to adduct formation processes. We also stress that, although the Z-open tautomers are intrinsically more electrophilic than furanone ring analogues, the observed mutagenic activity is significantly correlated only to the electrophilicity response of the ring forms. In that context, we also emphasize that it is electrophilicity at the C (alpha) in the alpha-beta unsaturated carbonyl moiety that exhibits a strong correlation with the observed mutagenic activity.