Multifrequency phase fluorometry was used to determine the lifetime distributions of 1,6 diphenyl-1,3,5-hexatriene in 1-palmitoyl-2 linoleoyl phosphatidylcholine small unilamellar vesicles containing 2% incorporation of phospholipid hydroperoxides. A biexponential decay was observed in both vesicle preparations over a temperature range of 5 to 35 degrees C. Vesicles containing phospholipid hydroperoxides showed an overall longer lifetime as well as a greater distribution in width. These findings suggest that phospholipid hydroperoxides create structural heterogeneity in membrane structure.