Low density lipoproteins (LDL) were isolated from nonhuman primates fed isocaloric diets rich in different types of fatty acids. These diets contained 35% of calories as fat enriched in fatty acids from the following sources: lard that is rich in saturated fatty acids, safflower oil rich in oleic acid, safflower oil rich in linoleic acid and menhaden oil that is rich in n-3 fatty acids. LDL composition reflected the dietary fats. LDL were subjected to oxidation using copper ions and azobis(2-amidinopropane) x 2HCl. In general, the sensitivity of LDL to oxidation depended on both the poly-unsaturated fatty acid and vitamin E content. However, the lag times calculated for the copper ion catalyzed oxidations did not show the linear dependence on vitamin E content that was found for azobis(2-amidinopropane) catalyzed oxidation.