We present a sensitive method for the determination of cefaclor (CCL), a beta-lactam antibiotic. It was based on the chemical derivatization of the drug with 4-(2'-cyanoisoindolyl)phenylisothiocynate (CIPIC) under the reaction conditions with heating at 80 degrees C for 7 min in the presence of pyridine. The CIPIC reagent could react with the primary amino group of the drug to form the CIPIC-conjugated CCL. The derivatives emitted not only fluorescence (FL) at maximum emission wavelength of 410 nm with irradiation at 310 nm, but also chemiluminescence (CL) in the presence of H(2)O(2), borate buffer (pH 9.6) and acetonitrile. After separation of the CIPIC derivatives of CCL and cephradine as internal standard in human serum by reversed-phase liquid chromatography, the derivatives could be monitored with both FL and CL detections. The detection limit (S/N=3) in the chromatograph was 1 pmol by the CL detection and 10 pmol by the FL detection. The proposed CL method permitted the most sensitive determination of CCL in the human serum after its oral administration.