The purpose of this study was to assess the joint cartilage's capacity for repair and the potential of various biological tissues as replacements for damaged cartilage. METHODS: We operated 30.3 months old, lambs, creating a chondral lesion which was left untreated in group I and treated with a fresh chondral implant in group III, a frozen chondral implant in group IV, and a frozen periostal implant in group V; in group II the lesion extended as far as the subchondral bone. The lesions were performed in the loading area of the medial condyle of the knee. Follow-up time was 6 months, and the results were assessed histologically. RESULTS: In the chondral lesions which remained untreated (group I), degeneration of the exposed layers occurred, and loss of both cartilage thickness and homogeneity of the matrix was noted. Where the lesion extended as far as the subchondral bone (group II), repair was found to have taken place with a fibrous tissue indistinguishable from cartilage. When cartilage was implanted (group III and IV), the integration of the implant depended on wether there was any contact between the implant and the surrounding tissue. DISCUSSION: The integrity of the fresh implants was maintained better than that of the frozen ones, which were found to contain cells with a proliferative capacity. When periosteum was placed over the chondral lesion, we observed the formation of a very loose fibrous tissue in which the initial stages of differentiation could be appreciated in the deepest layers.