Detailed investigation was made of the triacylglycerol structure of native, simulated, and interesterified peanut oils, which had previously been shown to differ markedly in their atherogenic potential. By means of chromatographic and stereospecific analyses, it was shown that the more atherogenic native oil contains a significantly greater proportion of triacylglycerols with linoleic insn-2-position and arachidic, behenic, and lignoceric acids insn-3-position than the synthetic oils. It is suggested that the atherogenicity may arise from a relative metabolic unavailability of the linoleic acid from the native oil, which may be due in part to the presence of long chain saturated acids in the outer position. This might render the oil metabolically more saturated than the interesterified oils of the same total fatty acid composition, which contain a much greater proportion of the linoleic acid in the primary positions of the triacylglycerol molecule. The identification of specific triacylglycerols may allow the experimental testing of this hypothesis by feeding synthetic triacylglycerols incorporating the potentially atherogenic features.