Cytologic examinations of kidneys, which were frozen for preservation in a nitrogen atmosphere below 3 ata, show a considerable damage of the cells. This does not only occur by significant reduction in the amount of isolated cells, but also in the loss of the ability to form cell colonies. DNA measurements show, however, that after 3–4 days the DNA amounts in surviving cells are intact. In one of the cultures we even found DNA values, which stand for a DNA synthesis. Experiments with mechanical perfusion alone show that this procedure results in a severe damage of the cells, only about one-third of these cells being able to form colonies.