Transfer of cefotetan (CTT) into exudates from excoriated skin wounds was studied in 9 adult patients. Each subject was given an intravenous bolus injection of 50 mg/kg of body weight. Concentrations of CTT in serum and in exudate fluid were determined by bioassay using Escherichia coli NIHJ as the test organism. The mean (+/- S.D.) CTT concentration in serum reached 274.3 +/- 78.3 micrograms/ml at 30 minutes after the injection and decreased to 30.0 +/- 12.0 micrograms/ml at 8 hours after the injection. The peak value of CTT in exudate fluid was 143.1 +/- 22.3 micrograms/ml at 1 hour. Eight hours after the injection, the mean concentration in the exudate was 25.7 +/- 21.1 micrograms/ml. The data obtained were analysed pharmacokinetically: CTT concentrations in serum were analysed by two-compartment model, and those in exudate fluid from excoriated skin wounds were analysed by the model in which skin was considered as a small part of the peripheral compartment. Thus T1/2(beta) of CTT levels in serum was calculated as 2.38 hours, AUC0----infinity was 1,000.2 micrograms X hr/ml and Vd was 164.5 ml/kg. Tmax and Cmax of CTT levels in exudates were calculated as 1.05 hours and 131.2 micrograms/ml, respectively.