The transfer of cefoperazone into exudates from excoriated skin wounds was studied in 13 adolescent and adult patients. Subjects were given an intravenous bolus injection of 50 mg/kg of body weight. Concentrations of cefoperazone in serum and in exudate fluids were determined by bioassay using Escherichia coli as the test organism. Mean (+/- SD) cefoperazone concentration in serum reached 333.3 +/- 103.3 micrograms/ml 30 minutes after the injection and decreased to 16.4 +/- 5.7 micrograms/ml eight hours after the injection. In exudate fluids, the peak value was 52.7 +/- 22.1 micrograms/ml at one hour. Eight hours after the injection, the mean concentration in the exudate was 10.7 +/- 7.2 micrograms/ml, which was considerably above the minimum inhibitory concentrations for important pathogens.