A specific anti-apoE2(Arg158→Cys) monoclonal antibody was raised by means of immunization of mice with a variant specific synthetic peptide. The peptide sequences used were homologous to apolipoprotein E of human and mouse. Consequently, the mouse immune system was tolerant to most of the selected sequences. Immunization with only one of selected peptides (amino acids 154-172) evoked an anti-peptide and anti-native protein response. Surprisingly, this peptide was predicted to have a low antigenicity index, in contrast to the other used peptides. The variant specific anti-peptide MAb that was generated with this sequence, recognizes apoE2(Arg158→Cys) and not apoE3. We here describe a sensitive, time saving, and simple immunoblot assay to detect apoE2(Arg158→Cys) in human sera without prior isoelectric focusing of serum proteins. Chemicals/CAS: arginine, 1119-34-2, 15595-35-4, 7004-12-8, 74-79-3; cysteine, 4371-52-2, 52-89-1, 52-90-4; Antibodies, Monoclonal; apolipoprotein E-2; apolipoprotein E-3; Apolipoproteins E; Arginine, 74-79-3; Cysteine, 52-90-4; Epitopes