Abstract A method to measure racemic, R- and S-ifosfamide concentrations from the serum of patients receiving ifosfamide chemotherapy has been developed. The racemic ifosfamide concentrations are quantified on a separate system and then the ratio of the enantiomers is determined using an achiral—chiral coupled system. Racemic ifosfamide is separated on the achiral system using a C 1 spherisorb stationary phase and the eluent containing analyte is selectively transferred to the chiral system for separation of the two enantiomers by an α 1 glycoprotein column. On both systems the mobile phase is 1% acetonitrite in 0.015 M phosphate buffer (pH 4) at a flow-rate of 1 ml/min. The retention times of S- and R-ifosfamide were 11.6 and 13.0 mins, respectively, with a resolution factor of 1.53. Serum concentrations at least three to four half-lives post-infusion were detected by this method. In ten patients, following a mean ± S.D. 1-h infusion of 3.9 ± 0.32 g racemic ifosfamide, the mean ± S.D. clearances of R- and S-ifosfamide were 0.061 ± 0.013 and 0.072 ± 0.014 l h −1 kg −1.