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The relative importance of chylomicrons (Sf greater than 400) and very low density lipoproteins (Sf 20--400) in transporting lipids in lymph was investigated in surgically prepared adult sheep and pre-ruminant lambs fed low fat diets or infused intraduodenally with corn oil. The concentration of triacylglycerol in the intestinal lymph of sheep and lambs was increased from 520 and 925 mg/100 ml to 2326 and 2367 mg/100 ml respectively when corn oil was infused into the duodenum and the ratio of triacylglycerol to phospholipid changed from 3.7 and 5.5 to 9.5 and 9.7 respectively. The flow of lymph also increased. Electron microscopy and analytical and preparative ultracentrifugation showed that lymph lipoproteins from sheep and lambs fed low fat diets consisted mainly of lipoproteins 50 nm in diameter and that very low density lipoproteins (Sf 20--400) contirbuted up to 75% of the Sf greater than 20 lipoproteins. There were no lipoproteins with diameters above 150 nm. Infusion of corn oil into the duodenum of sheep and lambs increased the diameters of lymph lipoproteins. Most were 80--100 nm in diameter but substantial numbers above 150 and up to 400 mn were observed. The maximum contribution of very low density lipoproteins (Sf 20--400) to lipoproteins of Sf greater than 20 was 27--30%. The above findings demonstrate that the size of intestinal lymph lipoprotein particles increases with the amount of lipid absorbed from the small intestines and that the transport of lymph lipids, in ruminants, is similar to that previously found in rats, rabbits and man.