Perichondrium from rabbit auricular or rib cartilage was used as a free autogenous graft and transplanted either to the subcutaneous tissue of the back of the rabbit or to an experimental defect in the femur condyles. Outgrowth of new tissue, morphologically indistinguishable from cartilage, was observed after six weeks. Inorganic ³⁵SO₄, administered in vivo, was incorporated into the newly formed tissue. The labelled products were isolated, identified, and compared with those obtained from authentic cartilage of auricular, rib or joint surfaces. The products of newly formed cartilage were similar to those of authentic cartilage. The results support earlier morphological findings, indicating that perichondrium from rib cartilage has a better ability to regenerate than auricular perichondrium. The synovial environment seems to have a positive effect on the generation of cartilage.