The amino acid sequence of porcine and human caseinomacropeptides (CMP), the C-terminal glycopeptide released from kappa-casein by chymosin at the initial step of milk coagulation, have been investigated. The complete amino acid sequence of porcine CMP and that of the first 59 amino acid residues of human CMP have been determined. Porcine and human CMPs contain 71 and likely 65 amino acid residues respectively. The extra hexapeptide 38-43 found in porcine CMP arises obviously from the duplication of the DNA fragment coding for the 6 preceding amino acids.