Aortic tissue of adult New-Zealand male and female white rabbits was studied. After thin-layer chromatography of cholesterol esters, triglycerides, free fatty acids, phosphatidylethanolamines and phosphatidylcholines, their fatty acid compositions are determined. Phosphatidylcholines and phosphatidylethanolamines contain important quantities of arachidonic acid. The level of linoleic acid in these phospholipids is higher in male animals than in female. Conversely the level of arachidonic acid is higher in females than in males.