A “new” allotypic specificity of rabbit immunoglobulins (A14) is described. The determinant is localized on the Fc portion of heavy chains of rabbit γG. The specificity is inherited in a simple Mendelian manner and the gene controlling its synthesis is localized at the locus Ae, which is distinct from Aa and Ab loci; the product of the gene allelic to the Ae14 gene is not yet known. There is a strong indication that the loci Ae and Aa are closely linked in the germline, but that they may undergo recombination in the somatic cells, thus causing the synthesis of recombinant molecules.