To study whether free-grafted perichondrium would produce new cartilage, perichondrium taken from the rabbits' ears was transplanted to the subcutaneous tissues of the groin and the back, to the muscles of the back, to the areolar tissue in the neck, and to the parenchyma of the liver. A clot of blood was placed in close contact with the perichondrium at randomly selected recipient sites. Wherever the perichondrium was grafted in the presence of clotted blood new cartilage was produced, irrespective of age and weight of the rabbit. When blood was withheld, little or no cartilage formed. New formation of cartilage began in the first week after transplantation and the cartilage was mature within 7 weeks.