This IgG preparation is intended for use as a control for primary antibodies made in mouse. Supplied as a lyophilized powder, this antibody has been purified from pooled serum of healthy adult animals and contains a spectrum of the IgG subclasses present in serum. The control antibody should be applied to the tissue section at the same concentration as the primary antibody to indicate whether staining is specific for the antigen or is nonspecific adsorption of primary antibody to tissue sites.