Lipids and oxidised lipids were analysed by GC and GC-MS in samples of human atheroma (necrotic gruel from the interior of advanced atherosclerotic plaques in the aorta) and human normal aorta (lesion-free intima plus inner media) from necropsy subjects. Cholest-5-en-3 beta,26-diol and cholest-5-en-3 beta,7 beta-diol were detected in all the atheroma samples examined but not in significant amounts in normal aorta. In atheroma, cholest-5-en-3 beta,26-diol was approximately proportional to cholesterol. Several isomeric hydroxy-octadecadienoic acids were detected in atheroma, and, in smaller amounts, in normal aorta. Many of the components of atheroma showed a high degree of cross-correlation on linear regression analysis, whilst cross-correlations were somewhat weaker for normal aorta. Atheroma showed a vast accumulation of lipid, especially cholesterol, in comparison to normal aorta. The atheroma samples contained a larger proportion of linoleate relative to oleate than the normal aorta. Levels of fatty acids relative to cholesterol were lower for atheroma than for normal aorta. The chemical composition of atheroma appeared unrelated to the age of the subject, whereas age-related increases in linoleate, oleate and cholesterol content were seen in the samples of normal aorta.