During development, mRNA for matrix metalloproteinase‐13 (MMP‐13) is found associated with cartilage undergoing hypertrophy, suggesting that this collagenase plays a role in cell enlargement and/or cartilage calcification. Using chondrocytes from prehypertrophic cartilage of chick embryo sternae, we have examined the relationship between MMP‐13 expression and the transition to hypertrophy. When hypertrophy was induced by serum‐free culture with ascorbate and bone morphogenetic protein‐2 (BMP‐2), MMP‐13 mRNA levels paralleled those for type X collagen. Chondrocytes from the caudal, nonhypertrophying portion of chick sternae expressed neither type X collagen nor MMP‐13, confirming that MMP‐13 mRNA is a marker for hypertrophy. Zymography with conditioned medium yielded a proteinase band at 59 kDa, which was absent in nonhypertrophic chondrocytes. A polyclonal antibody raised against chick MMP‐13 reacted with the 59‐kDa protein, confirming that it is MMP‐13. Although mRNA for MMP‐13 peaked at days 4–5 of culture, only low levels of MMP‐13 activity were present, and the activity increased gradually in parallel with later increases in MMP‐2. These results suggest that MMP‐13 is activated by MMP‐2 during chondrocyte maturation, and that the combination of both proteinases is required to prepare cartilage matrix for subsequent calcification, before endochondral ossification. J. Cell. Biochem. 77:678–693, 2000. © 2000 Wiley‐Liss, Inc.