Survival prolongation was studied in rats which were hemodiluted to a hematocrit value of as low as 7, 4 or 1% by stepwise exchange transfusion, alternating bleeding through the artery and infusing a perfluorochemical (FC) emulsion into the vein, with the combined use of oncotic agents taken into consideration to maintain the circulating plasma volume. Plasma expander (PE) was indispensable to the use of FC emulsion for the survival of exchange-transfused rats. As an oncotic agent to be combined with FC emulsion, homologous plasma and 6% hydroxyethyl-starch (HES) solution were better than dextran in rats. At the exchange transfusion with FC emulsion + PE, totaling 1.2 times the volume of blood eliminated, survival effect was better at a ratio of FC emulsion to PE to 1:3 than 3:1. Supplementary infusions of Fluosol-DA (an improved FC emulsion made isooncotic with 2.7% HES) carried out after the exchange transfusion at intervals of 24 h were effective in prolongation of survival.