The amino acid sequence of caprine [Capra hircus] CMP [caseinomacropeptide], the negatively charged C-terminal fragment released by chymosin (rennin EC 3.4.23.4) from goat K-casein at the initial stage of the milk-clotting process, was investigated. The complete sequence was determined by analyzing chymotryptic and thermolysin fragments of CMP. Caprine CMP contains 66 amino acid residues, with 2 phosphorylated, Asp2, Asn5, Thr11, Ser6, SerP2, Glu7, Gln2, Pro6, Ala9, Val5, Met1, Ile6, Lys3, His1; the carbohydrate-free polypeptide chain has a MW of 6998 daltons. The occurrence in caprine CMP of an additional phosphate group, linked to serine 168 in the C-terminal region Thr-Ser168-Thr-Glu170-Val OH of the polypeptide chain, gives support to the phosphorylation code for caseins postulated earlier. According to this hypothesis, a specific phosphoryl kinase may recognize an anionic phosphorylation site corresponding to the tripeptide sequence Thr/Ser-X-Glu, X being any amino acid residue. Since the C-terminal sequence of bovine and caprine CMP differ by the substitution Ala/Glu170 (caprine), phosphorylation of caprine serine 168 could be explained by the occurrence of the new phosphorylation site Ser168-Thr-Glu170.