The aim of this study was to define a two-compartments pharmacokinetic model and to estimate the pharmacokinetic parameters of IP administered vancomycin in patients with continuous ambulatory peritoneal dialysis (CAPD) associated peritonitis. Ten patients with peritoneal dialysis treatment and peritonitis were prospectively enrolled in the study. The empiric treatment is: vancomycin 2 g every 5-7 days and ceftazidime 1500 mg per exchange, once daily. Pharmacokinetic modeling and parameter calculations were carried out using the nonlinear regression. The mean peritoneal concentration 10 min after the first peritoneal exchange of vancomycin free dialysis liquid was 9.5±7.3 μg/ml, showing that antibiotic quickly crosses from "systemic" to "peritoneal" compartment. Then, we can appreciate a progressive reduction in the mean peritoneal concentration till last sample time at 168 h. The mean plasma concentration 4 h after the first peritoneal exchange of vancomycin-free dialysis liquid was 39.6±7.6 μg/ml, inside classic interval therapeutic range for the peak concentration of vancomycin. Then, we can appreciate a progressive reduction in the mean plasma concentration till last sample time at 168 h. Simultaneous joint analysis of the experimental plasma and peritoneal data of vancomycin in patients under CAPD with peritonitis, using the two-compartments model, sets up a physiologic model that adapts suitably to the intraperitoneal pharmacotherapy.