Acid soluble collagen and purified alpha1 and alpha2 chains were prepared from bovine skin and digested with cyanogen bromide. The resultant peptides were separated by electrophoresis on polyacrylamide gels containing sodium dodecylsulphate. Thirteen peptides obtained from the alpha1 chain and two from the alpha2 chain were identified as overlapping sequences containing methionine-derived peptide bonds not cleaved during the reaction. Those uncleaved peptides from the alpha1 chain accounted for approximately 30% of the total digest, as determined by planimetry on the staining profiles, and their relative proportions indicated that efficiency of cleavage at specific methionine residues was dependent upon position in the sequence. Alpha1CB5-8 was most resistant to cleavage while alpha1CB0,1-2 and alpha1CB7-6 were most susceptible. Peptides of a 2:1 (w/w) mixture of alpha1 and alpha2 chains and of the acid-soluble collagen gave electrophoretograms which were essentially a summation of those obtained from the individual chains.