1. Irradiated ergosterol given by mouth to rabbits, in doses of three milligrams daily, did not increase the rate of healing or the amount of callus formed in fractures of the tibia and fibula.
2. Irradiated ergosterol given to rats with the food, in doses of one and twenty-five one-hundredths milligrams daily, did not increase the rate of healing or amount of callus formed in fractures of the fibula.
3. There is some evidence that the administration of irradiated ergosterol to animals by mouth will produce calcification in blood vessels and other soft tissues.
4. The most significant factor in the rate of healing and in the union of experimental fractures in animals is the degree of apposition of the fragments of bone.