COMP (Cartilage Oligomeric Matrix Protein) is a non-collagenous protein in the matrix of the joint cartilage. The molecule is a large protein (524 kDa) consisting of five identical disulfide-linked subunits.

COMP is believed to have a role in the assembly and stabilization of the extracellular matrix in the joint cartilage by binding and cross-linking of collagen fibrils.

It is a well-known phenomenon that cartilage, when broken down by a disease process, releases protein fragments (matrix proteins) into the synovial fluid. These fragments can later on be detected in blood and urine.