FT-IR and ESR were used for on the investigation of the CCl_4-induced peroxidation of rat liver microsomes in combination with biochemical methods. Lipid peroxidation was assayed by TBA reagent in the presence of CCl_4 and NADPH. The CCl_3 radical was detected by ESR spectroscopy with a spin trapping reagent of PBN. The FT-IR spectroscopy revealed that absorption band of -C-H in -C=C-H decreased in intensity at 3012 cm^, but the absorption bands of the phosphate head and choline in the phospholipids did not significantly change between 1300 and 900 cm^. These findings were interpreted to be due to the removal of H from -C=C-H by radicals as the first step of lipid peroxidation, and to the absence of dephosphorylation of phospholipids in the microsomal membrane. This is the first IR spectroscopic evidence indicating the nature of damage to a microsomal membrane caused by CCl_4 treatment. The spectroscopies used here demonstrated that they are useful tools to observe the damage to microsomal membranes
