Abstract The ears of sixty-two rabbits were immersed for one minute in a freezing mixture cooled to −50 °C., then rapidly thawed for two minutes in a water bath heated to +42 °C. One group of rabbits (31) received 1.0 γ per kilogram of Piromen (a bacterial polysaccharide) per animal intravenously daily for thirty days; placebo injections of sodium-R-lactate (0.1 ml. per kilogram) were given intravenously to animals 31 in a second group. Of the rabbits given rapid thaw therapy and placebo, 32 per cent suffered no loss of exposed tissue by amputation, but the ears were nonvital in appearance. Animals given rapid thaw therapy and Piromen approached 100 per cent recovery, these ears being in excellent condition. It appears that Piromen enhanced the effectiveness of rapid warming of rabbit ears exposed to freezing temperatures.