Abstract: Preservation of biological materials is accomplished by apparatus and a process with and by which the material is cooled at a substantially linear rate to approximately freezing temperature, changed from the liquid to the solid phase at relatively constant temperature, and cooled at a substantially linear rate to an end temperature. The environment surrounding the material is rapidly chilled when the material reaches freezing temperature or a temperature minimally warmer than freezing temperature in the liquid phase to initiate phase change with minimal risk of super cooling the material, and is then warmed to freezing temperature or a temperature minimally cooler than freezing temperature to minimize temperature drop in the material upon completion of phase change. The apparatus contemplates, among other things, preselection of cooling rates, duration of phase change, and the end temperature.