Summary In rabbits the hepatic artery was ligated and necrosis of the liver and Clostridium welchii infection followed. The action of hyperbaric oxygen treatment at 3 ATA, the effect of antibiotics and the combination of both were studied. If the treatment with hyperbaric oxygen was started within two hours after ligation of the hepatic artery, the infection with clostridia could be partially prevented. The necrosis of the liver was not prevented by this therapy. Treatment with hyperbaric oxygen starting six hours after the ligation of the hepatic artery had no effect on the mortality and number of positive cultures. The action of antibiotics was studied. These drugs produced a decrease in mortality and in the number of infections with Clostridium welchii. The differences were significant in the streptomycin group. The action of antibiotic therapy and hyperpressure in combination was significantly effective in prevention of Clostridium infection; there was, however, no reduction in mortality nor in prevention of the liver necrosis. The effect of hyperbaric oxygen therapy could be explained as a temporary arterialization of the portal vein.