The murine monoclonal antibody HRS-3 (Ab1; isotype IgG1-Kappa), that defines the CD30 antigen (m.w. 120,000) expressed by Hodgkin-Reed Sternberg cells was used to generate monoclonal anti-idiotype antibodies (Ab2) in syngeneic BALB/c mice. Ab2 were selected on the basis of their binding to HRS-3 immunoglobulin and F(ab')2 fragments and lack of reactivity with the whole immunoglobulin or F(ab')2 fragments of unrelated monoclonal antibodies of the same isotype and allotype. Such a putative anti-idiotypic Ab2, was designated antibody 12D3 and further characterized. 12D3 bound to the paratope of HRS-3, as determined by a 85% inhibition of binding of biotinylated HRS-3 to the cell surface of the CD30 positive Hodgkin cell line L450, and to semipurified CD30 positive cell lysates thereof at a concentration as low as 50 ng/well. These results demonstrate that 12D3 binds at or near the binding site of HRS-3 to the CD30 antigen. Purified 12D3 was coupled to keyhole limpet hemocyanine and used to immunize BALB/c mice and rabbits in order to obtain an Ab3 which binds to the CD30 antigen. These immune sera inhibited the binding of biotinylated 12D3 with HRS-3. Moreover, they showed binding activity with the CD30 positive L540 Hodgkin cell line as well as with the L540 cell lysates, indicating that an anti-anti-idiotopic antibody (Ab3) shares idiotopes with Ab1 (HRS-3). These data suggest that antibody 12D3 may be useful in the generation of an anti-idiotype vaccine against Hodgkin's lymphomas.