The simultaneous detection of the phase I metabolite of coumarin, 7-hydroxycoumarin, and the two phase II metabolites, 7-hydroxycoumarin-glucuronide and 7-hydroxycoumarin-sulphate by capillary electrophoresis with UV detection using liver slice incubations was investigated. Separation was carried out on an untreated fused silica capillary with detection at 320 nm. Separation was achieved in under 6 min with a total run time of 8 min. Both phase two metabolites were produced following an in vitro incubation of liver slices in Krebs-Hanseleit buffer with 100 microM 7-hydroxycoumarin. Limits of detection were 5.52 microM (2 micrograms ml-1) for the glucuronide, 2.21 microM (0.5 microgram ml-1) for the sulphate and 6.17 microM (1 microgram ml)-1 for 7-hydroxycoumarin. Mean inter- and intra-assay results are presented for all three analytes, respectively.