AbstractThe objective of this study was to determine the feasibility of using a fluorocarbon liquid in a liquid‐liquid contacting device for extracorporeal blood oxygenation. Extraction experiments were carried out wherein blood was gently contacted with FC‐43 (a fluorinated tributyl amine) for up to 48 hr. The fluorocarbon caused no significant change in red cell volume, white cell count, plasma hemoglobin, platelet count, plasma fibrinogen, or the relative amounts of thirteen different plasma proteins. To determine toxicity, FC‐43 slugs and emulsions were injected intravenously and intraaortically into dogs. No chemical toxicity has been found, but the fluorocarbon is intolerable above about 1.7 mg/kg because it retards the flow of blood through pulmonary capillaries. FC‐43 was used for several in vivo tests of a vertical cylindrical blood oxygenator. The hemolysis caused by the falling film of fluorocarbon on the inner Teflon wall of the cylinder was considerably less than that caused by direct contact between blood and Teflon, suggesting that the blood‐fluorocarbon interface is quite atraumatic. All these results indicate that this fluorocarbon liquid holds considerable promise for use in a liquid–liquid blood oxygenator.