In the knee joints of adult rabbits osteochondral defects of 4 mm in diameter were placed by a drill reaching the cancellous bone. In the first group the defects were left untreated or closed by collagen foam or by fibrin adhesive or a combination of both. In the second group the defects were closed with very small autologous cartilage fragments and fibrin adhesive. The animals were observed over up to 40 weeks. In the first group no hyaline cartilage was found histologically in any of the defects. In the second group a rapid proliferation of chondrocytes appeared with development of hyaline cartilage with alcian-blue-positive matrix. It resembled juvenile cartilage in its histologic appearance and with regard to the induction of ossification. This phenomenon is interpreted as a "second adolescence" of the adult cartilage induced by the rich nutritional and oxygen supply from the cancellous vessels, which resembles the environmental conditions before forming of subchondral cortical bone at the end of the growth period. This method enabled us to achieve a complete closure of defects by hyaline cartilage on the very level of the surrounding articular surface.