The amino-acid sequence of the gamma-carboxyglutamic acid-containing protein of bovine bone is presented. The sequence of 43 of the 49 residues was determined automatically on the intact protein and on a tryptic peptide. The remainder was determined by conventional procedures on tryptic and chymotrytic peptides. Residue 9 in the sequence has been identified as 4-hydroxyproline. The protein contains three gamma-carboxyglutamic acid residues, which are located at positions 17, 21, and 24. The role of these unusual amino acids in the binding interaction between the protein and hydroxyapatite crystals is discussed.