alpha 2(I) chains of chicken bone collagen were isolated and purified. Analyses confirmed previous studies that the alpha 2(I) chains contained gamma-glutamyl phosphate residues. Sodium borohydride reduction of the gamma-glutamyl phosphate residues of the CaCl2 extracted and purified alpha 2(I) chains and subsequent CNBr cleavage showed that most of the gamma-glutamyl phosphate groups were located on the alpha 2CB3-5 peptides of the type I collagen molecule, suggesting a specific function for these phosphorylated residues. The reported linkage of the Ser(P) containing phosphoproteins of dentin to the alpha 2CB4 regions of collagen may indicate different biological functions for these two different, protein-bound organic phosphate residues.