The catalytic domain of matrix metalloproteinase-10 (MMP-10) has been expressed in Escherichia coli and its crystal structure solved at 2.1 A resolution. The availability of this structure allowed us to critically examine the small differences existing between the catalytic domains of MMP-3 and MMP-10, which show the highest sequence identity among all MMPs. Furthermore, the binding mode of N-isobutyl-N-[4-methoxyphenylsulfonyl]glycyl hydroxamic acid (NNGH), which is one of the most known commercial inhibitors of MMPs, is described for the first time.