Mono(2-ethylhexyl) phthalate was given to guinea pigs and mice and its metabolites were isolated from urine. A procedure consisting of sorbent extraction, ion-exchange chromatography and reversed-phase high-performance liquid chromatography was used in the purification scheme. The metabolites were analysed by fast atom bombardment mass spectrometry. It is concluded that the purification procedure is very mild and that fast atom bombardment is a useful ionization technique for intact conjugates of metabolites of bis(2-ethylhexyl) phthalate.