1. The viability and general preservation of skin that has been subjected in vitro to freezing, drying and other procedures may be tested by transplanting it back to the animal from which it was originally removed.

2. Rabbit's ear skin withstands either slow or rapid freezing down to the temperature of liquid air.

3. Slow freezing gives better preservation than rapid freezing, but impregnation with glycerol solutions protects skin against some of the harmful consequences of rapid freezing. Epidermal melanoblasts do not withstand rapid freezing unless they have been protected by glycerol solutions.

4. Rapid thawing gives better preservation than slow thawing. Malpighian cells of the epidermis survive slow thawing after impregnation with glycerol solutions but not after impregnation with Ringer's solution.

5. Skin slowly frozen after impregnation with glycerol solution and stored for 4 months at -79°C. was indistinguishable, on transplantation, from a freshly removed graft. The storage of skin at -79°C. does not result in progressive deterioration during the period of storage.

6. It is shown that the toxicity of glycerol to the various cellular constituents of skin is so slight that it may be disregarded. Isolated epidermal cells withstand exposure to 98.1% glycerol at room temperature for half an hour.

7. Skin does not withstand dehydration to a degree that results in a final overall water content below about 25%. Impregnation with glycerol solutions does not increase its capacity to withstand dehydration.

British Empire Cancer Campaign Research Fellow.