1. Detailed studies have been made of the plasma lipoprotein abnormalities in parenchymal liver disease to test the hypothesis that the abnormalities would correlate with plasma lecithin-cholesterol acyltransferase (LCAT) activity. 2. When LCAT was high, very-low-density-lipo-proteins (VLDL) were normal in composition and had a normal pre-β electrophoretic mobility. When LCAT was low, VLDL concentrations were greatly reduced. 3. With high LCAT low-density lipoproteins (LDL) were normal. The LDL particles found with low LCAT activity were of normal size but of abnormal composition, being triglyceride rich and cholesteryl ester poor. Regardless of LCAT activity LDL were present in normal amounts. 4. High-density lipoproteins (HDL) were normal in composition and electron-microscopic appearance when LCAT activity was high. When LCAT activity was low HDL were abnormal in composition and ‘stacked discs’ were seen on electron microscopy. 5. These results suggest that low LCAT activity may be the cause of at least some of the lipoprotein changes of parenchymal liver disease.

1. We have studied the plasma lipoprotein abnormalities in obstructive jaundice to test the hypothesis that the abnormalities would correlate with plasma lecithin—cholesterol acyltransferase activity. 2. Very-low-density lipoproteins (VLDL) were normal in composition and had a normal pre-β electrophoretic mobility when lecithin—cholesterol acyltransferase activity was high. When it was low VLDL had abnormal composition and ran in the β position. 3. With high lecithin—cholesterol acyltransferase activity, low-density lipoprotein (LDL) was normal and cholestatic LDL (LP-X) was not found. With low lecithin—cholesterol acyltransferase activity up to three LDL fractions were found: (i) large triglyceride-rich particles, (ii) LP-X and (iii) a triglyceride-rich cholesteryl ester-poor particle of normal dimensions. 4. High-density lipoprotein (HDL) concentrations correlated with lecithin—cholesterol acyltransferase activity and HDL were normal in composition and electron-microscopic appearance when the activity was high. When lecithin—cholesterol acyltransferase activity was low HDL was abnormal in composition and ‘stacked discs’ were seen on electron microscopy as well as normal spherical particles. 5. These results suggest that low lecithin—cholesterol acyltransferase activity may cause at least some of the lipoprotein changes of obstructive jaundice.