Analysis of sequence alignments between the recently published sequence of human fibroblast collagenase and a computer file of published protease sequences has revealed a previously unrecognized homology to the 11 amino acids flanking the zinc-binding site of Serratia protease, a bacterial metalloprotease. There is also strong homology among several bacterial metalloproteases at this site. This finding implies that zinc binding by many proteins may have structural requirements which are apparent even in primary structure and which have been evolutionarily conserved or convergently evolved. This consensus sequence could be used as a marker for recognizing other members of the metalloprotease family.