We studied the kinetics of piperacillin in patients under continuous ambulatory peritoneal dialysis. Piperacillin 2 g was injected intravenously in 6 patients whereas 1 g was given intraperitoneally either a single dose in 3 patients without infection or the same dose every six-hours in 4 patients with peritonitis. Piperacillin was assayed by HPLC. After intravenous administration, the mean plasma piperacillin concentration was 3.1 +/- 5.6 mg/l at 12 h, the mean plasma t1/2 at 2.43 +/- 0.84 h, the volume of distribution at 20.4 +/- 6.3 l and the peritoneal clearance at 0.19 +/- 0.04 ml/min. After iterative intraperitoneal administration, serum and dialysate concentrations of piperacillin were above the minimum inhibitory concentration for susceptible pathogens without antibiotic accumulation. Peritoneal absorption was higher during peritonitis (83.4 +/- 4.8%) than without peritonitis (67.8 +/- 8.5%). Piperacillin 2 g IV every 8 hours or 1 g IP every 6 hours seemed to be the appropriate regimen in patients with chronic renal failure on CAPD.