With the recent development of technics [sp] for transplanting human tumors to the cheek pouch of.cortisone-treated hamsters, it has become possible to test the response of human tissues under the conditions of hibernation. During the past year we have tested five transplantable human tumors. Our results indicate that the growth of this tissue from a homeothermic mammal is markedly inhibited by hibernation, but that the tumor survives after prolonged exposure to these low temperatures. Our primary reason for carrying out this study was to test the possibility that the growth rate of these heterologous tumors might be slowed down sufficiently to provide a means of temporarily "storing" transplantable human tumors.