A rapid high-performance liquid chromatographic method is described for the simultaneous determination of carbamazepine and the 10,11-epoxide, 10,11-dihydroxy, and 2-hydroxy metabolites of carbamazepine. The chromatographic system involves the use of a 18C-microsorb, reversed-phase column with acetonitrile/water (28:72) as the mobile phase. Detection and quantitation are monitored by ultraviolet absorption at 212 nm. The compounds are extracted from 250 microliters of plasma or from 100 microliters urine with methyl-t-butyl ether and 0.1 M sodium hydroxide; 2-methylcarbamazepine is added as internal standard. If phenytoin and/or phenobarbital are present in plasma or urine samples, it is necessary to use 1.0 M sodium hydroxide. The limits of quantitation for carbamazepine and its metabolites are 10 ng/ml.