A simple, accurate and precise isocratic reversed-phase high-performance liquid chromatographic method has been developed and validated for the determination of a new cephalosporin in human serum and urine. Human serum samples, calibration standards and quality control samples (250 microliter) were combined with an equal volume of 6% trichloroacetic acid (TCA). Human urine (0.1 ml) was combined with 6% TCA solution containing the internal standard. The compounds were detected by ultraviolet absorbance set to 280 nm for the serum assay and 313 nm for the urine assay. The method for the determination of cefixime in serum was linear from 100 ng/ml to 30.0 micrograms/ml (r = 0.999), and for the urine assay from 5 micrograms/ml to 100 micrograms/ml (r = 0.999). The minimum reportable quantity for the serum assay was 0.05 microgram/ml. The within- and between-day assay variation for both assays were found to be less than 10% in an extensive assay validation scheme. Results of a storage stability study indicated that human serum and urine samples could be safely stored for up to six months at -18 degrees C and three months at -10 degrees C, respectively.