Continuing refinement of fluorocarbon blood substitutes depends upon perfection and application of methods to monitor oxygen transport in living animals. Methods involving chronic catheterization, electrode implantation and tissue sampling yield valuable basic information in animal experiments. The importance of blood lactate in assessing the adequacy of fluorocarbon oxygen transport is reported here. The preliminary observation of microbubble blockade in the pulmonary capillaries in rabbits receiving F-decalin (PP5) emulsion, resulting in lungs which remain noncollapsible for at least 79 days is also reported.