Broad-spectrum antibiotics (cephalothin, ampicillin, tetracycline, and two forms of chloramphenicol) were administered intraperitoneally during peritoneal dialysis to patients with essentially no renal function. Significant serum levels were obtained with all drugs tested except chloramphenicol succinate. Despite continuing intraperitoneal administration for 18 to 32 hours, all drugs except tetracycline demonstrated a leveling off of serum levels. The dangers of administration of tetracycline during peritoneal dialysis are emphasized. The dynamics of peritoneal absorption, pharmacology, and toxicity are discussed and recommendations are made regarding choice and dosage of appropriate antibiotics.