Summary Thin-layer chromatography has been used to gain a roughly quantitative impression of the phospholipid distribution within the human chylomicron and of the phospholipid mixture present in various animal materials. The phospholipids of chylomicrons obtained following a fat meal were similar in distribution to those of total human plasma, and comprised phosphatidyl choline, sphingomyelins, phosphatidyl ethanolamine and lyso-phosphatidyl choline. Hen egg-yolk phospholipids showed a higher content of phosphatidyl ethanolamine but lower amounts of sphingomyelins. The sera of the sheep, steer and hog were examined, and of these the phospholipids of the last were closest in composition to those of the chylomicron. It is suggested that hog serum phospholipids may provide a physiologically acceptable emulsifying system for use in intravenous fat emulsions.