The peptide Val–Arg–Arg–Pro–Asn–Leu–His–Pro–Ser–Phe–Ile–Ala–Ile–Pro–Pro–Lys–Lys–Ile, which corresponds to residues 84–101 of human κ-casein, has been synthesized and its conformation preferences determined by 1H-nuclear magnetic resonance spectroscopy in dimethyl sulphoxide. The peptide adopted a largely extended chain conformation in solution and there was evidence for the presence of a β-turn involving residues Pro87–His90 of human κ-casein. The presence of a turn in this position would make the physiologically significant Arg85 residue of human κ-casein (which is equivalent to Arg97 in bovine κ-casein) unavailable for interaction with Asp249of bovine chymosin, and may partly explain why human κ-casein is hydrolysed more slowly than its bovine counterpart by bovine chymosin.