Abstract: To gain more insight into the molecular mechanisms of chondrogenic differentiation induced by transforming growth factor (TGF)-β1 and insulin-like growth factor (IGF)-I and insulin, we performed cDNA microarray experiments during the chondrogenic differentiation of human mesenchymal stem cells (hMSCs), which provide an excellent in vitro model system for chondrogenesis. Our repeated cDNA microarray analyses identified the up regulation of 23 transcripts and the down regulation of 25 transcripts after 14 days of chondrogenic induction. We found that many of the up regulated and down regulated genes belonged to overlapping gene categories; specifically, 44 and 40% of the up regulated and down regulated genes were associated with the extracellular matrix and metabolic pathways, respectively. The expression of the identified genes was confirmed by RT-PCR. These analyses suggest that the transcriptional control induced by TGF-β1, IGF-I and insulin signaling during the chondrogenic differentiation of hMSCs is mainly targeted to genes belonging to specialized gene categories.