Abstract: A family of metalloproteinases exist which cleave extracellular matrix molecules. These metalloproteinases are secreted in a latent inactive form and require activation in order to specifically cleave the preferred substrate. A series of peptides have been prepared based on the complete sequence analysis of type IV procollagenase. Peptide inhibitors were synthesized which correspond to cysteine repeat regions and histidine containing regions; the mechanism of action of these peptides involves inhibition of binding of the enzyme to the substrate. Peptide inhibitors were synthesized which correspond to the peptide cleaved off during activation, and constitute a novel class of metalloproteinase inhibitors. These inhibitors are members of a series of peptides which contain the core amino acid sequence RKPRC or analogs thereof. The cysteine residue is required for activity.