The electron impact mass spectra of conjugated bile acids, their 5alpha-analogs and methyl esters of glyco conjugates were determined by direct insertion into the ion source and their fragmentation patterns were found to be basically similar to those of methyl esters of the free bile acids. The conjugates are additionally characterized by a significant loss of [NH2CH2CO2H] from the glycine moiety and [CH2 = CHSO3 H] from the taurine group. Several 5 alpha- and 5 beta-isomers can be differentiated, but no general pattern of recognition is discernable. Field desorption mass spectra contain [M + Na]+ and [m + Na]2+ ions.