Samples of bovine caseinomacropeptide (CMP) were isolated from κ-casein A and κ-casein B and fractionated to give aglycosylated CMP A and CMP B and monoglycosylated CMP A. The secondary structures of these three peptides were compared under neutral and acidic (pH 4·2) conditions, using two-dimensional (2D) 1H nuclear magnetic resonance (NMR) spectroscopy. The differences between the spectra at pH 4·2 and 7·0 and the spectra of the aglycosylated and glycosylated CMP A were subtle, indicating little change in backbone conformation with these changes. These results suggest that differences in the coagulation properties of milks containing either κ-casein A or κ-casein B are more likely to be related to factors, such as micelle size or charge, than to structural differences arising from altered backbone conformation of the macropeptide segments of the κ-caseins.