Serum amyloid P component (SAP) is a normal plasma protein and a universal non-fibrillar constituent of amyloid deposits. SAP is a member of the pentraxin protein family which includes Creactive protein. Human SAP is secreted and catabolized only by hepatocytes, and consists of five identical non-covalently associated subunits, each with a molecular mass of 25 kDa, which are non-covalently associated in a pentameric disc-like ring. SAP is a calcium-dependent ligand binding protein, which binds to DNA and chromatin, and to all known types of amyloid fibrils accounting for its specific accumulation in amyloid deposits. Serum amyloid P component scintigraphy is a non-invasive and quantitative method for imaging amyloid deposits, which produces diagnostic images in most patients with systemic amyloidosis, and can be used repeatedly to monitor the course of the disease.