Twenty one murine monoclonal antibodies (MAbs) were produced against bovine -casein (-CN). Eight epitopic groups of MAbs recognising six discrete determinants (4-8, 14-24, 33-48, 49-91, 177-183, 184-209) were defined from ELISA reactivity with peptides and related homologues from 3 species (ovine, human and equine). Thirteen distinct epitopes were discriminated by cross-examination of the MAbs reactivity in BIAcore. Determinants 14-24, 49-91 and 184-209 were found to encompass at lest 4, 2 and 4 epitopes respectively. No MAb was bovine specific, but one at least discriminated ovine/caprine casein from bovine. Terminal sequences 1-28 and 177-209 included ~80% of the discriminated epitopes, and the most conserved ones. This panel of MAbs can provide specific probes for -CN proteolysis fragments.