A high-performance liquid chromatographic method for the determination of a new-broad spectrum cephalosporin (I, SCE-2787) has been developed. The analyte was extracted from serum by precipitation of serum proteins with acetonitrile. Acetonitrile was extracted from the protein-free supernatant by dichloromethane. Urine was simply diluted with mobile phase. Separation was performed by ion-pair chromatography on a reversed-phase column (Nucleosil 5C18; 125 mm x 4.0 mm I.D.; 5 microns average particle size). The guard column was Perisorb RP18 (30 mm x 4.0 mm I.D.; 30-40 microns particle size). The mobile phase was acetonitrile-buffer solution containing 15 mM heptanesulphonic acid (pH 3.2) (4.5:95.5, v/v). Detection was performed at 235 nm with a diode-array detector, which also served to record ultraviolet spectra. The assay was sensitive, precise, accurate and fast. Specificity was controlled by on-line recording the ultraviolet spectrum of I and also by enzymic degradation with beta-lactamase. No interferences were observed during the analysis of serum and urine of healthy volunteers in pharmacokinetic studies.