The effects of elevation of the perichondrium of the nasal septum, whether or not followed by resection of the cartilage, was histologically studied in young rabbits. The perichondrium has proved to be a highly reactive tissue. The degree of reaction varied from a transient oedema to the production of large quantities of cells, differentiating into new cartilage. The type of reaction appeared to depend on the conditions at the inner surface of the elevated perichondrium. The new cartilage differs from the original septal cartilage in morphology and growth potential. The data described above can contribute to the interpretation of previous observations in children.