Serum amyloid A1 (SAA1) is a protein that in humans is encoded by the SAA1 gene. SAA1 is a major acute-phase protein mainly produced by hepatocytes in response to infection, tissue injury and malignancy. When released into blood circulation, SAA1 is present as an apolipoprotein associated with high-density lipoprotein (HDL). SAA1 is a major precursor of amyloid A (AA), the deposit of which leads to inflammatory amyloidosis. As a result, SAA1 has been a clinical indicator and reliable biomarker for inflammatory diseases, chronic metabolic disorders and late-stage malignancy. Inflammatory amyloidosis results from chronic inflammation with increased production of SAA1, which is a major precursor of amyloid A fibril deposit in various tissues. SAA1 has been extensively studied for its binding to HDL, with results suggesting a role in lipid metabolism. During the acute-phase response, elevated levels of SAA1 in the plasma displaces ApoA-I and becomes a major apolipoprotein of HDL.