The peritoneal transport of vancomycin during peritoneal dialysis was studied in 11 uremic patients following intravenous and intraperitoneal administration of vancomycin. The half-life of vancomycin was about 18 h and the clearance of vancomycin 6.1 ml/min (range 4.2--9.8) during the period of dialysis. Following intraperitoneal administration of vancomycin 50 micrograms/ml of dialysate, serum concentrations from 5.1 to 21.5 micrograms/ml were obtained and 35% of the instilled amount of vancomycin was absorbed during 15 h of dialysis. The peritoneal transport of vancomycin indicates that the dosage should be increased during peritoneal dialysis. Peritonitis caused by Staphylococcus aureus may be treated by peritoneal dialysis with vancomycin added to the dialysate.