Mesenchymal stem cells derived from human bone marrow (hBM-MSCs) can differentiate into chondrogenic cells for the potential treatment of injured articular cartilage. To evaluate agarose gels as a supportive material for chondrogenesis of hBM-MSCs, this study examined chondrogenesis of hBM-MSCs in the agarose cultures. Pellet cultures were employed to confirm the chondrogenic potential of the hBM-MSCs that were used in agarose cultures. The hBM-MSCs were seeded in 2% agarose constructs at the initial cell-seeding densities of 3, 6, and 9 × 106 cells/ml while each of pellets was formed using 2. 5 × 10+ cells. Chondrogenesis of hBM-MSCs was induced by culturing cell-agarose constructs and pellets for 21 days in the presence of a defined medium containing transforming growth factor β3 (TGF-β3). The analysis of reverse transcription-polymerase chain reaction showed that hBM-MSCs of agarose and pellet cultures expressed the chondrogenic markers of collagen type II and aggrecan in the presence of TGF-β3. The deposition of cartilage-specific macromolecules was detected in both agarose and pellet cultures by histological and immunohistochemical assessments. Chondrogenesis of hBM-MSCs in agarose gels directly correlated with the initial cell-seeding density, with the cell-agarose constructs of higher initial cell-seeding density exhibiting more cartilage-specific gene expressions. This study establishes a basic model for future studies on chondrogenesis of hBM-MSCs using the agarose cultures. © 2004 Wiley-Liss, Inc.