Human lactotransferrin contains six residues of methionine per mol. Seven different fragments were characterized after treatment with cyanogen bromide (CNBr) and large parts of their sequences were determined. The alignment of the CNBr fragments was established by the determination of N- and C-terminal sequences, by the study of the C-terminal domain obtained by peptic digestion of the protein and by taking into account the internal homology as well as homology with human serum transferrin. The two glycopeptides were situated in the N- and C-terminal parts of the protein, respectively, a situation quite different from that encountered in serum transferrin. The sequence studies allowed us to suggest a 4- and perhaps 6-fold internal homology.