A high-pressure liquid chromatography (HPLC) method that successfully measured cefoxitin (a modification of the antibiotic cephamycin C) levels in subcutaneous tissue, muscle, and aortic and peripheral arterial walls has been developed. Samples were obtained from 11 patients submitted to prosthetic aortic replacement. All patients received an intravenous bolus dose of cefoxitin 2 g just before induction of anaesthesia. Blood and tissue samples were taken at various intervals intra-operatively. The tissue samples were mechanically homogenised. Both plasma and the tissue homogenates were deproteinated with trichloracetic acid. The cefoxitin was separated by HPLC and measured by ultraviolet absorbance. The results show that the tissue concentration of the drug fell over a 4-hour period and that all levels exceeded the MIC90 (minimum inhibitory concentration that inhibits growth of bacteria at the 90% level) for most aerobic and anaerobic pathogens for at least 3 hours.