Abstract
Plasma membrane is a primary site for freezing injury. By freezing, ultrastructure of plasma membranes shows diverse changes, such as intramembrane particle (IMP) aggregation, lamellar to hexagonal II phase transition, endoplasmic vesiculation, and formation of IMP-free patches. All these plasma membrane ultrastructural changes are closely related to the occurrence of freezing injury. It was suggested that freezing injury was caused by diverse mechanisms depending not only upon different freezing conditions but also upon difference of cell types.