Before being taken up by the liver, chylomicrons are hydrolyzed successively by two lipases. The first one is the lipoprotein lipase which hydrolyzes mainly chylomicron triacylglycerols and gives rise to remnant particles. The latters will be further hydrolyzed by the hepatic lipase which exerts mainly a phospholipase A1-like activity on these particles. Chylomicrons as well as remnants, incubated with hepatic lipase in vitro, lose up to 47% of their phospholipids while triacylglycerols are less or even not hydrolyzed at all. A decrease in phosphatidylcholine (-30% and -34%) and an increase in lysophosphatidylcholine (+260% and +316%) are the main modifications measured in chylomicrons and in their remnants respectively, after hepatic lipase action. From several date (Borensztajn's work and ours), it arises that phospholipolysis of chylomicrons and of chylomicron remnants, is the obligatory metabolic step before these particles are taken up and degraded by the liver.