Studies were carried out to determine the relationship between Fe(++)-ascorbate initiated chemiluminescence and lipid peroxidation in rat liver, lung, kidney and brain microsomes. In order to follow the time course of membrane lipid peroxidation, we measured simultaneously physical and biochemical changes. Thus we determined the fatty acid composition of microsomal membranes from those tissues after peroxidation with and without ascorbic acid. Fractionation of cytosolic proteins with ammonium sulfate 70% saturation yielded a soluble fraction (enriched in fatty acid binding protein) that inhibited ascorbate-Fe++ dependent lipid peroxidation. The inhibitory effect was concentration dependent and was not abolished by heating of the soluble fraction during 5 min at 100 degrees C. Preparations from kidney, lung, heart and brain showed similar effect on lipid peroxidation of liver microsomal membranes. It is especulated that retinyl esters bound to fatty acid binding protein may act as antioxidants against lipid peroxidation.