Homozygous rabbits genotypically different for the allotypy of the VH region and the C kappa region of their immunoglobulins (al/al, b4/b4 and a3/a3, b5/b5, respectively) were transferred together at the blastocyst stage to be born from the same foster mother. At the time of transfer the foster mothers were active anti-anti-idiotypic (Ab3) antibody producers and, according to their own genotype, the idiotypes (Ab1) which initiated the immunization cascade ending with their Ab3 were allotypically either a1,b4 or a3,b5. This experimental scheme was carried out, at the level of the Ab1 and of the Ab'1 (antibodies produced by the transferred rabbits subjected to the Ab3 action), with three different exogenous antigens, namely a protein, a polysaccharide and a hapten which elicited in normal rabbits the production of antibodies with private idiotypic specificities. Two of them, the protein and the polysaccharide enabled us to find idiotypic relationships between antibodies totally different for their allotypy and particularly for the allotypy of the variable region of their heavy chains. In these examples, the structural coercions implied by the different allotypic markers of the VH did not seem to prevent the association of at least related genetic elements responsible for the observed idiotypic community. In these idiotypic relationships, only subpopulations of the Ab1 and of the Ab'1 were implicated and they could be different for the diverse littermates.