Fluosol-DA, 20%, a perfluorochemical whole blood substitute, was infused during Phase II and Phase III clinical trials at 24 medical institutions in Japan to 185 patients for replacement of blood lost during surgery or for improvement of cerebral circulation. Its active ingredients (perfluorodecalin, perfluorotripropylamine, hydroxyethyl starch and Krebs-Ringer bicarbonate solution) give this biologically inert emulsion not only plasma-expanding properties but also a high oxygen-carrying capacity (7.2 vol.% at 37 degrees C; the oxygen carrying capacity of red blood cells is 17 to 20 vol.%). Doses given to the patients ranged from 6 to 25 ml/kg body weight. With regard to arterial blood oxygen tension, arterial blood oxygen content, blood oxygen transport, oxygen consumption, and acid-base balance, beneficial effects were generally observed after infusion of the emulsion following blood loss especially when the fractional concentration of oxygen in inspired gas (FiO2) was kept higher than 0.5. The emulsion also manifested beneficial plasma-expander effects on hemodynamics (blood pressure, pulse rate, and central venous pressure). In no case was there any anaphylactoid or other untoward reaction observed or reported during or after infusion of the emulsion. Although a slight prolongation of bleeding time (Duke) was found, the surgeons never experienced and hemorrhagic tendencies during or after their operations. Slight and transient elevations of SGOT were found but SGPT and alkaline phosphatase levels remained normal. All other hematological and biochemical parameters measured in blood, serum and urine remained within normal ranges.