Respiration and oxidative phosphorylation were studied in liver mitochondria of rats with experimental peritonitis. Peritonitis did not cause any distinct alterations in the functional state of liver mitochondria. Activity of main mitochondrial enzymes was only slightly altered. Inactivation of metabolic toxins occurred in cytoplasm of hepatocytes, i. e. out of mitochondria. Addition of peritoneal exudate at various dilutions to intact isolated mitochondria caused uncoupling of respiration and oxidative phosphorylation.