This paper describes a method which permits the absolute identification of Hb D-Los Angeles Bithout the need for N-terminal or amino acid analysis on peptideβT-13. The procedure involves the formation of the 5-oxo-2-pyrrolidinecarboxylyl derivative of the N-terminal glutamine residue ofβDT-13. This method, together with the use of cadmium ncetate/ninhydrin staining, allows the identification of Hb D-Los Angeles, and other possible mutntions of p121, by peptide mapping.