Laying hens are highly cost-effective as producers of antibodies compared with the mammals traditionally used for such production. Also, chicken antibodies have biochemical advantages over mammalian antibodies due to the phylogenetical differences between avian and mammalian species, resulting in increased sensitivity as well as decreased background in immunological assays. In contrast to mammalian antibodies, chicken antibodies do not activate the human complement system nor will they react with rheumatoid factors, human anti-mouse IgG antibodies, or bacterial and human Fc (fragment crystallizable)-receptors. Thus, chicken antibodies offer many advantages over mammalian antibodies and may replace such antibodies in the future.