Whole IgG antibodies are isolated as intact molecules from antisera by immunoaffinity chromatography. They have an Fc portion and two antigen binding Fab portions joined together by disulfide bonds and therefore they are divalent. The average molecular weight is reported to be about 160 kDa. The whole IgG form of antibodies is suitable for the majority of immunodetection procedures and is the most cost effective. PAP soluble immune complexes are prepared by the method of Sternberger et al. (J. Histochem. Cytochem. 1970. 18, 315). Theoretically, they consist predominantly of two anti-horseradish peroxidase antibodies in soluble complex with three molecules of horseradish peroxidase.-