Cholesterol preserved in archaeological bones and teeth constitutes an important new source of palaeodietary information. A method is described here for the isotopic (delta13C) determination of cholesterol employing a semiautomated sample preparation procedure and the technique of isotope ratio monitoring/gas chromatography/mass spectrometry (irm/GC/MS). High-temperature gas chromatography (HT-GC) and high-temperature gas chromatography/mass spectrometry (HT-GC/MS) were used to identify the lipids and quantify the cholesterol present in the total lipid extracts. Delta13C values are then readily obtained from nanogram amounts (~50 ng) of cholesterol resolved and determined directly by high-resolution capillary irm/GC/MS of trimethylsilylated total lipid extracts. The protocol developed allows effective processing of the large numbers of samples essential for palaeodietary determinations. Analytical precision and reproducibility have been assessed through multiple sampling of the same skeleton (femur, 9th century). Comparable delta13C values have been obtained from different skeletal members from the same individual. The utility of the approach is demonstrated through a study of the delta13C values of cholesterol isolated from sections of femoral bones of individuals excavated from cemeteries (dated Saxon to 18th century) at a coastal site in the U.K. The mean delta13C value (-22.2 +/-0.3, S.D.= 0.9) determined for cholesterol in 50 different individuals indicates a strong preference for marine foods by the members of the community extending back over the last ~1500 years. A minority of individuals exhibited 13C values as low as -26, indicating preferences for terrestrial rather than marine foodstuffs.