A synthetic peptide, reproducing the first five amino acid residues of the gamma(2)-casein sequence, was formylated to generate the novel haptenic structure, already well-recognized in formaldehyde-treated milk and arising out of molecular rearrangement after the addition of formaldehyde to the alpha-amino group of the histidine residue at the N terminus of gamma(2)-casein.     ///    Immunochemical detection of formylated gamma(2)-casein in cheese..     ///    A polyclonal antibodies preparation produced against the formylated peptide adduct proved to be a highly specific analytical tool for detecting the formylated adduct of gamma(2)-casein in formaldehyde-treated milk.     ///    Polyclonal antibodies obtained against the unmodified peptide were able to detect selectively residual native gamma(2)-casein in ripened cheese.. 