Abstract: The new technique of fast atom bombardment mass spectrometry has.been applied to the investigation of some free bile acids and their succinyl derivatives using glycerol or thioglycbl as "matrix compatible solvent".The pseudomoiecular species are observed giving molecular weight information.In negative ion mass spectra the(M-1)-ion is the most intense ion which is the base peak for each of the samples.Additionally,dimer ions and adduct ions with species which are from the matrix are obtained with low intensity.The technique allows the determination of the mixture of bile acids and the pseudomoiecular species observed to give molecular weight information for the component.