To examine the repair collagens produced by cells in injured cartilage, the femoral articular surfaces of three groups of New Zealand white rabbits were injured by making both superficial and deep lacerations and drill holes. Eight weeks after surgery, the rabbits were killed and slices of injured articular cartilage were harvested. The types of collagen being synthesized at the site of these lesions were identified by labeling the recovered specimens in vitro with 3H-proline and by characterizing the collagen using sodium dodecyl sulphate electrophoresis, carboxymethyl cellulose chromatography, and cyanogen bromide peptide analysis. In all cases, tissue-specific type II ([alpha1 (II)]3) cartilage collagen was synthesized. Histological examination using toluidine blue showed that the chondrocytes bordering the cartilage defect produced by deep lacerations and drill holes responded by increased cellular activity, as shown by cell cloning and increased matrix staining. The drilled holes were completely filled by tissue with staining and morphological characteristics similar to those of hyaline cartilage.