In anesthetized, oxygen-breathing rabbits, the entire blood volume was exchanged with a 20% colloidal fluorocarbon fluid suspension of high gas solubility. In contrast to the control animals with acute isovolemic and hypervolemic hemodilution, the fluorocarbon suspension prevented the decrease in arterial oxygen content below a hematocrit of 13%. However, the more pronounced effect of the fluorocarbon suspension on oxygen delivery occurred at higher hematocrits and was due to its efficiency as a plasma expander, since it increased the cardiac output even above the level of the hypervolemic hemodilution group. The fluorocarbon suspension also raised arterial blood pressure and total peripheral resistance due to its increased viscosity. Thus, in mild hemodilution, the fluorocarbon suspension kept oxygen utilization in the normal range by increasing cardiac output, and in extreme hemodilution it improved oxygen utilization by also raising the arterial oxygen content and arterial blood pressure. The survival time of the isovolemic control animals was 31.6 min, it was extended to 57.8 min in the hypervolemic control animals, and the rabbits with the fluorocarbon suspension lived for 124.8 min.