A number of studies over the past four decades1-3 have documented the role of bacteria, especially that of Clostridium welchii, in the pathogenesis and mortality of bile peritonitis in dogs. It has been shown that bile peritonitis, known to be lethal in dogs, does not kill germ-free dogs.4 The well-recognized bacteriostatic effect of high pressure oxygen (HPO) on C welchii organisms5,6 stimulated us to investigate the possible effect of HPO on experimental bile peritonitis in dogs. In addition, we attempted to correlate the level of intraperitoneal oxygen tensions with changes in survival rates. Methods Under intravenously administered sodium pentobarbital anesthesia and utilizing aseptic techniques, the abdomen of each dog was opened through a midline incision. The gallbladder was aspirated until it collapsed, and the bile was cultured under anaerobic conditions. The fundus of the gallbladder was excised and the edge of the open sac was everted with