Chickens produce an immunoglobulin G (IgG) homologue, sometimes referred to as IgY (to reflect the differences in the heavy chain domain compared with mammalian IgG), which can be conveniently isolated from the yolk of eggs (1). The concentration of immunoglobulin in the egg yolk is roughly the same as in serum (10-15 mg/mL), and an average egg can yield approx 80-100 mg of immunoglobulin. Eggs can therefore provide an abundant source of polyclonal antibody that may be aquired noninvasively from eggs laid by immunized chickens (2). The production of polyclonal antibodies in chickens provides other advantages over using conventional mammalian species. The mechanism of antibody production and organization of the avian immune system is quite different from that of mammals, and as chickens are phylogenetically distant from mammals because of their evolutionary divergence millions of years ago, it is possible to generate antibody responses to highly conserved proteins that do not easily elicit an immune response in mammalian species. Chicken immunoglobulins possess other characteristics that differ from mammalian antibodies that may offer advantages in certain immunological techniques. Most of the interactions via the Fc region in mammalian antibodies do not occur with chicken immunoglobulin. Chicken IgG does not activate mammalian complement systems, and does not react with mammalian rheumatoid factors, and neither protein A or protein G bind to chicken IgG. Although chicken antibodies can be substituted for mammalian antibodies in many techniques (and may even be advantageous) it may be necessary to optimize conditions in certain systems particularly with precipitation techniques where chicken IgG appears to be less efficient then conventional mammalian polyclonal antibodies.