The pharmacokinetics of vancomycin were studied in continuous ambulatory peritoneal dialysis patients with peritonitis. Six patients received an intraperitoneal loading dose of 15 mg/kg and 4 received an intraperitoneal dose of 25 mg/L. The ability of 2 methods to predict serum concentrations during the loading dose exchange was determined. The mean serum concentration after the exchange was 17.8 ± 2.2 mg/L in patients receiving the loading dose. The mean dialysis clearance in all patients was 0.94 ± 0.34 L/h. 66.6 ± 13.4% of a dose was absorbed into the circulation in 4h. The volume of distribution was 0.61 ± 0.46 L/kg, and the half-life for equilibration of vancomycin into the circulation from dialysate was 2.76 ± 0.94h. Two methods of predicting serum vancomycin concentrations were tested, with 1 method predicting values significantly different from measured concentrations while the other did not. Serum vancomycin concentrations can be accurately predicted during a loading dose exchange.