Osteogenic protein-1 (OP-1, BMP-7), a member of the transforming growth factor-beta family, induces cartilage and bone formation when implanted at intra and extraskeletal sites in vivo. The human OP-1 gene has been cloned and biologically active recombinant OP-1 homodimers have been produced. In the present study, the authors investigated the influence of OP-1 on healing of full-thickness articular cartilage defects, made by drilling two adjacent (phi 3mm) holes through articular cartilage of NZW rabbit knee joint were dissected and examined histomorphometrically. Results indicated that OP-1 induced articular cartilage healing and regeneration of the joint surface which contained cells resembling mature joint chondrocytes. These data imply a new strategy for biological repair of damaged joint surfaces in humans.