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Successful application of tissue-engineering techniques to damaged biological structures is determined by functional performance in vivo. This study evaluated the in vivo response of a tissue-engineered construct composed of a polylactic acid–alginate amalgam seeded with bone marrow-derived mesenchymal stem cells and stimulated in vitro with transforming growth factor β for cartilage tissue engineering. Constructs were placed in cylindrical osteochondral defects in the canine femoral condyle and examined 6 weeks postoperatively by gross, histological, immunohistochemical, and biomechanical analyses. In the course of 6 weeks in vivo, the defects filled with a cartilaginous tissue regardless of whether cell-seeded (experimental) or cell-free (control) constructs were implanted; however, the quality of the tissue differed between the experimental and control defects. Cell-seeded experimental defects showed more cartilage-like matrix quality, cell distribution, and proteoglycan staining. Biomechanically, experimental and control specimens exhibited similar behavior; however, both tissues were still immature compared with normal cartilage. The evidence accumulated in this study showed a modest acceleration of the in vivo healing of cellseeded constructs but also demonstrated a reparative response of cell-free constructs. This finding suggests that the constructs prepared from the PLA–alginate amalgam may serve as a means for host cell attachment.