High-field (63.4 kilogauss) Fourier transform nuclear magnetic resonance spectroscopy 13C in natural abundance has been used to study the structural organization and molecular dynamics of constituent lipids of normal human very low-density lipoproteins (VLDL) and low-density lipoproteins (LDL). The same method was used to study the abnormal beta-VLDL of two type III hyperlipoproteinemia patients having markedly differing ratios of VLDL cholesterol to triglyceride (0.3 and 0.6, respectively). Resolution obtained at 63.4 kilogauss has made possible the assignment of several additional resonances of cholesterol ring carbon atoms, not resolved in earlier studies at lower fields, in the VLDL spectra. The rotational reorientation of the ring portion of cholesteryl esters in VLDL (normal) and beta-VLDL (abnormal) is not highly anisotropic and is similar to that for cholesteryl esters disolved in excess triolein. The rotations of cholesteryl esters in LDL are more highly anisotropic and significantly more restricted. The results suggest that the structural organization of the lipid components in beta-VLDL resembles that found in normal VLDL but differs significantly from that for normal LDL.