Damaged articular cartilage rarely heals or regenerates in middle-aged and elderly adults, suggesting that the chondrogenic potential of mesenchymal stem cells declines with age. To test this hypothesis, we measured the responses of rat bone marrow-derived mesenchymal stem cells (BMSCs) to chondrogenic induction in vitro. BMSCs from immature rats (1 week old), young adult rats (12 weeks old), and old adult rats (1 year old) were analyzed for cartilage extracellular matrix (ECM) production. Histologic analysis showed strong cartilage ECM formation by BMSCs from 1-week-old rats, but not by BMSCs from 12-week-old or 1-year-old rats. Real-time polymerase chain reaction revealed age-related declines in messenger RNA encoding type II collagen, aggrecan, and link protein, three major cartilage ECM components. Microarray analysis indicated significant age-related differences in the expression of genes that influence cartilage ECM formation. These findings support the hypothesis that the chondrogenic potential of mesenchymal stem cells declines with age.