Two hapten-inhibitable murine monoclonal antiidiotopic antibodies identified two idiotopes expressed by the heavy chain of hybridoma protein 36-65, whose amino acid sequence is encoded in the germ line of A/J mice. Among cross-reactive idiotype-positive hybridoma proteins and p-azophenylarsonate-immune antibodies, the two idiotopes were not always expressed together; some diversified antibodies expressed one idiotope without the other. Suppression that was induced by the two antiidiotopes was idiotope specific and corresponded to the fine specificities of these two reagents.