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The complete amino acid sequence of bovine α-lactalbumin has been established. The unique sequence was deduced by characterization of the tryptic, chymotryptic, and peptic peptides isolated from enzymic hydrolysates of the two unique fragments obtained on cleavage of S-aminoethyl-α-lactalbumin with cyanogen bromide as described earlier. Important overlapping peptides were also obtained by sequence analysis of peptic and chymotryptic peptides isolated from unmodified or S-carboxymethyl-α-lactalbumin. Bovine α-lactalbumin contains 123 residues with NH₂-terminal glutamic acid and COOH-terminal leucine. In accord with earlier reports, bovine α-lactalbumin has a considerable similarity in sequence to hen egg-white lysozyme. Alignment of the sequences of these two proteins shows that 49 of the residues are identical and an additional 23 residues are conservative replacements.