When producing peptide-antibodies, it is important to use a carrier protein to elicit a better response from the animal. Commonly used carrier proteins are BSA and KLH, with KLH preferred for its higher immunogenicity. Peptides coupled with BSA will generate antibodies against both the peptide and the BSA, which could result in incorrect ELISA readings. For coupling carrier proteins to peptides, we recommend incorporating an N terminus cysteine for this reaction due to the high efficiency and proven effectiveness. For coupling through cysteine, we use MBS (maleimidobenzoic acid-N-hydroxysuccinimide ester) as a crosslinker. The initial step is to activate the protein with MBS, and then remove the excess crosslinker by SEC. This activated carrier protein is then coupled to the cysteine in the peptide through a disulfide bond with an efficiency of >95%. The only impurity in this reaction is salt formation, which we remove through gel filtration. As an alternative to coupling through cysteine, we can additionally couple the carrier protein of choice through an amino link. The coupling efficiency of this reaction is generally around 80%. For carrying out this reaction, glutaraldehyde is used to crosslink the amino groups in both peptide and carrier protein. The most undesirable part of this reaction is the fact that protein-protein and peptide-peptide crosslinking can occur, and for this reason, the most important step is to insure that the proper concentration of crosslinker.