Reagents used in IHC methods should be fresh, not outdated, and prepared with clean, ultrapure, or distilled water. Reagents can be purchased prepared or in single chemical packages for mixing just prior to use. Whether the reagents are purchased or mixed in the laboratory, they should be of the highest quality possible. Repeating IHC due to poor quality reagents is expensive in both direct cost and personnel hours. Reagents, if not fresh or made properly, can greatly alter the attachment of the antibody to the antigen. Inappropriately prepared, managed, or concentrated wash reagents may dilute antibodies, complexes, and chromogens to the point of false-negative staining, increased background, and possibly non-specific staining.