This study aimed to examine the peritoneal penetration and pharmacodynamic exposure of intravenous cefozopran. Cefozopran 1 g was administered to 10 patients before abdominal surgery. Venous blood and peritoneal fluid (PF) samples were obtained at the end of the 0.5-h infusion and at 1, 2, 3, 4, 5 and 6 h thereafter. Drug concentrations in plasma and PF were determined, analysed pharmacokinetically and used for a Monte Carlo simulation with minimum inhibitory concentration (MIC) data. Cefozopran penetrated well into PF, with a mean (+/-standard deviation) maximum drug concentration in PF/plasma ratio of 0.65+/-0.17 (n=10) and area under the concentration-time curve ratio of 0.92+/-0.13. The probabilities of attaining the pharmacodynamic exposure target (PTA), defined as 70% of the time above the MIC, in PF were almost identical to those in plasma. The PTAs were 95-100% against Escherichia coli, Enterobacter spp. and Staphylococcus aureus with 0.5 g every 12 h; however, 1 g every 8 h or 1 g every 6 h was required for 93-98% PTA against Pseudomonas aeruginosa. These results should help us to understand the peritoneal pharmacokinetics of cefozopran whilst also helping to choose the appropriate dosage for surgical intra-abdominal infections.