The collagenase subfamily of matrix metalloproteinases (MMP) have important roles in the remodelling of collagenous matrices. The proteinaseactivated receptor (PAR) family have a unique mechanism of activation requiring proteolysis of an extracellular domain forming a neo-N terminus which acts as a tethered ligand, a process that has been associated with the development of arthritis. Canonical PAR2 activation typically occurs via a serine proteinase at Arg 36 -Ser 37 , but other proteinases can cleave PARs downstream of the tethered ligand and "disarm" the receptor. To identify additional cleavage sites within PAR2, we synthesised a 42-amino acid peptide corresponding to the extracellular region. We observed that all three soluble MMP collagenases -MMP-1, MMP-8, and MMP-13cleave PAR2 and discovered a novel cleavage site (Ser 37 -Leu 38 ). Metalloproteinases from resorbing bovine nasal cartilage and recombinant human collagenases could cleave a quenched fluorescent peptide mimicking the canonical PAR2 activation region, and kinetic constants were determined. In PAR2overexpressing SW1353 chondrocytes, we demonstrated that the activator peptide SLIGKV-NH 2 in-