We report the first specific human immunoglobulin subclass probe which was obtained by subcloning the gamma 3 hinge region. This specific γ3 probe allowed us to identify with certainty the Cγ3 gene on Southern genomic blots to describe the first Cγ3 restriction fragment length polymorphism (EZZ γ3 RF) and to show that an IgG3 selective deficiency previously described serologically was not due to a deletion of the C3 gene. Such a probe should be particularly useful for screening libraries from individuals with IgG3 immunodeficiencies or presenting unusual Cγ3 genes and consequently for studying the Cγ gene evolution. Immunoglobulin IgCH gene (Human) Gm allotype Restriction fragment length polymorphism Immunoglobulin G3 deficiency Hinge
