The complete amino acid sequence of major acute phase α1-protein of the rat (MAP) was derived from the nucleotide sequence of cloned cDNA. Amino acid analysis and partial sequencing supported the predicted sequence. The amino acid compositions of MAP and rat low-Mr kininogen are identical within experimental variation. The sequence is homologous (60%) to that of bovine low-Mr kininogen and both proteins carry the sequence for the vasoactive nonapeptide bradykinin in their C-terminal region. The rate of synthesis of MAP and the levels of MAP mRNA change coordinately during the acute phase response to inflammation. Major acute phase protein Bradykinin Kininogen Protein-biosynthesis regulation Acute phase reaction Inflammation.