A method is described for the separation of ketonic from non-ketonic bile acids. Oximes are prepared from the methyl esters and are subjected to chromatography on the lipophilic strong cation exchanger sulphohydroxypropyl Sephadex LH-20 (SP-LH-20) in the H+ form. Three fractions are obtained which contain non-ketonic compounds, compounds having a 7- or 12-oxime but no 3-oxime group, and compounds having a 3-oxime group. These groups can be analysed as trimethylsilyl ethers by gas chromatography and gas chromatography-mass spectrometry by using fused-silica capillary columns with SE-30 as the stationary phase. The method was applied to the analysis of bile acids in faeces. The major 3-oxo acids found were 3-oxo-5 beta- and 12 alpha-hydroxy-3-oxo-5 beta-cholanoic acids. Smaller amounts of 3,12-dioxo-5 beta-cholanoic acid were present and 3-oxo-5 alpha-cholanoic and 3-oxo-4-cholenoic acids were also identified, but could not be quantified. Semiquantitative analyses indicated that bile acids with a 3-oxo group may constitute 1-20% of the corresponding 3 alpha-hydroxy bile acids.