Peritonitis has proven to be the major deterrent to the further growth of continuous ambulatory peritoneal dialysis (CAPD) as a treatment strategy for end-stage renal disease. The correct treatment of peritonitis remains unsettled as evidenced by the presence of advocates for oral, intravenous or intraperitoneal antibiotic administration. This study examines the pharmacokinetic parameters of intravenous vancomycin when employed in the therapy of peritonitis. One gram of intravenous vancomycin was administered during 7 episodes of peritonitis in 5 patients. Plasma and end-of-dwell dialysate levels were maintained above the minimum inhibitory concentration for Staphylococcus aureus and S. epidermidis for 7 days following this single dose of vancomycin. These data establish the existence of sustained intraperitoneal entry of intravenous vancomycin during peritonitis and raise for speculation its use as the sole therapy in most episodes of gram-positive peritonitis.