Abstract. This study compares the chondrogenic capacity of high density cultures prepared from either the develop-mentally younger, distal region or more advanced proximal region of stage 23/24 limb mesenchyme in high density cultures. Distal cultures undergo extensive chondrogenesis whether in F12 medium supplemented with 10% fetal calf serum, 5% fetal calf serum, or fibronectin. On the other hand, proximal cultures fail to undergo chondrogenesis in medium containing 10% fetal calf serum or fibronectin, but do form cartilage in medium containing a decreased serum concentration or no serum. Furthermore, if the cells are cultured at low densities in native type I collagen gels, proximal cells have a reduced chondrogenic capacity in the presence of fibronectin, while chondrogenesis by distal cells is unaffected by the addition of fibronectin. The results demonstrate that proximal and distal cells respond differentially to serum and to fibronectin, and they suggest that the response of the cell to prevalent components of the extracellular matrix might change with development.