The cyanogen bromide peptide alpha 1(III)CB5 is 237 amino acid residues in length and occupies position 552--788 along the alpha 1(III) chain. For sequence analysis alpha 1(III)CB5 was fragmented with hydroxylamine, protease from Staphylococcus aureus V8, trypsin and the arginine-specific enzyme from mouse submaxillary gland. The peptides obtained were separated using molecular and ion exchange chromatography and sequenced with the automated Edman degradation procedure.