Changes in lipoprotein metabolism after liver transplantation from living related donors were investigated in nine pediatric patients by means of biochemical and proton nuclear magnetic resonance (NMR) analyses of lipoprotein. NMR offers rapid and nondestructive measurement of lipoprotein. The ratio of esterified cholesterol to total cholesterol, expected to be a prognostic indicator after liver transplantation, was low before the operation (0.44) and recovered to over 0.6 at 3 weeks. The half line width of the methylene peak of lipoprotein, as measured by proton NMR, was correlated with the ratio of esterified cholesterol to total cholesterol. It is suggested that proton NMR analysis can provide information about the biophysical changes in lipoprotein associated with liver transplantation.