A rapid and simple capillary zone electrophoresis (CZE) method for the determination of terbinafine and eight of its main metabolites after incubation with rat hepatic S9 fraction was developed. The effect of the concentration and type of the running electrolyte as well as of the addition of an organic solvent were studied with emphasis on selectivity and sensitivity. All nine components obtained (unmetabolized terbinafine and up to eight of its metabolites) are baseline resolved in less than 4 minutes using a 0.05 M phosphate buffer (pH 2.2) without additives, after a solid-phase clean-up procedure of these in-vitro samples. In addition, under the conditions described, no endogenous components of the sample interfere at the detection wavelength chosen. After optimization of the separation conditions, some analytical characteristics of the developed CZE method were investigated. A limit of detection of only 0.08 lg/mL was obtained for terbinafine using a standard solution. Finally, the use of on-line CZE/ diode array detection enabled to identify tentatively the presence of unmetabolized parent terbinafine and its metabolites in the mixture of nine components separated.