In order to look for the position of amyloid P in the macromolecular connective tissue and extracellular matrix system, we performed binding studies involving affinity chromatography. Binding studies revealed the strong binding of fibronectin to amyloid P (S-AP). The fibronectin-amyloid P linkage was dissociated after elution with 2 M urea. Heparan sulfate, a major glycosaminoglycan of the extracellular matrix, showed strong binding to S-AP, which was dissociated at 3 M urea. Laminin, collagen type I and type IV, reduced and alkylated glomerular basement membranes as well as the glycosamino-glycans hyaluronic acid and chondroitin-4-sulfate failed to bind to S-AP. Our binding studies show that amyloid P can react strongly with extra cellular matrix proteins and can help to explain the presence of amyloid P in normal connective tissue.