A method for rapid freezing is described in which use is made of the good heat conducting properties of silver. The freezing was accomplished by bringing the tissue in contact with a polished silver surface at the temperature of liquid nitrogen either at atmospheric or reduced pressure. Helium gas flowing over this surface prevented the condensation of water or air on the silver. After freezing the tissue was placed in a substituting solvent. The best results were obtained with 2% osmium tetroxide in acetone at −85°C. The ultrastructure of the tissue was well preserved in a narrow surface layer only.