Normal serum is typically used for the blocking of non-specific antibody binding in tissue and cell staining as well as other immunoassays. Normal serum works by blocking the binding of Fc receptors in the sample to the primary and secondary antibodies, as well as blocking non-specific binding of the antibodies to the sample. The serum used for blocking is typically from the species in which the secondary antibody was raised. Our normal donkey, goat, rabbit, and mouse sera can be used directly for blocking or as a constituent of a blocking buffer.