Fourteen biopsies of cartilage and subchondral bone were taken from nine half-joint knee allografts 10 weeks to 8 years after the transplantation. Deep-frozen cadaver grafts were used to replace the defective half-joint after resection for bone tumour. The biopsies revealed a slow substitution of the dead grafted bone and cartilage. Subchondrally, signs of incorporation could be seen from 12 months on. The dead cartilage matrix degraded gradually and slow simultaneous regeneration was observed. Thus, fibrocartilage was seen on the articular surface of the graft at 12 months, chondrocytes were present at 18 months, but islands of hyaline cartilage were not seen earlier than 7 years after the transplantation. In accordance with the earlier clinical findings, the histological signs of rejection were minimal. The long-term result of half-joint allograft transplantation is obviously dependent on the cartilage component.