Using three different instruments, cryolesions were made in the skin of experimental animals (pigs) and the extent of necrosis was determined after one week. The most efficient device was a probe using liquid nitrogen; the amount of tissue killed varied directly with contact time. With all the instruments, a freeze of three minutes consistently led to full-thickness necrosis of the skin. The freeze-thaw-refreeze technique did not produce as much necrosis as a single continuous freeze of the same duration. Cryosurgery was used on 65 benign skin tumors in patients. Pain was minimal and the cosmetic results were excellent. The only difficulty with the method was that it occasionally failed to kill the lesion. For that reason, at present cryosurgery is recommended only for benign lesions. If one suspects that a tumor might be cancerous, it should be biopsied before freezing. If it proves to be malignant, further treatment (excisional or x-ray) should be considered strongly.