Fresh specimens may be frozen to prevent deterioration or to prepare them for preservation by freeze-drying. However, even at 0°C, very little water in most biological materials is actually frozen. Specimens held at freezing temperatures are still subject to protein and lipid changes and damage from the growth of microorganisms. Tissues may be severely damaged by ice formation. Freezing for specimen storage and freeze-drying for specimen preparation have only limited application, depending on the intended use of the specimens.