It has been reported that in a system containing microsomal phospholipids, nicotinomide adenine dinucleotide phosphate (NADPH), Fe3+ -ADP complex and cytochrome P-450 reductase (a reconstituted microsomal lipid peroxidation system), excited carbonyl species and singlet molecular oxygen, (1 O2 may generate according to Russell’s proposed mechanism (Reaction 1). In the present study, generation of excited carbonyls was verified by their energy being transferred to dyes containing heavy atoms in their molecules. A possible mechanism for the generation of excited species and the energy transfer from excited carbonyls to dye molecules leading to the formation of excited dye molecules is outlined on p. 370 where LH, L?, LOO?, L′=O* and Dye* represent unsaturated lipids, lipid radicals, lipid peroxy radicals, excited carbonyls in triplet states, and excited dye in singlet state Reaction 4 is forbidden, but proceeds because of heavy atom perturbation (1 ). Thus, the excited carbonyl species formed during lipid peroxidation may transfer their energy to dye molecules containing heavy atoms such as Rose Bengal to produce singlet dye molecule in excited state. The excited Rose Bengal then emits a photon to return to its ground state. The aim of this chapter is to describe the relationship between Rose Bengal-dependent luminescence and 02 consumption in a methemoglobin (MetHb)-induced lipid peroxidation system and demonstrate how the reaction is quenched by α-tocopherol or probucol present in phospholipid liposomes.