100% (w/v) fluorocarbon (FC) emulsions have recently been developed as contrast agents in diagnosis. It is shown in this paper that the 50% (w/v) (ca 27% of FC by volume) emulsions derived from them by addition of salts and oncotic agents lead to high survival ratios after near-total exchange perfusion of the rat, with a safe inspired oxygen fraction (FiO2) of 0.6.