In order to target NK cells against the Hodgkin's-derived cell line L540, we developed bispecific monoclonal antibodies (Bi-MAbs) by somatic hybridization of the 2 mouse hybridoma cell lines HRS-3 and A9 which produce monoclonal antibodies (MAbs) with reactivity against the Hodgkin and Reed-Sternberg cell-associated CD30 antigen and the CDl6 antigen (Fcylll receptor), respectively. The CD 16 MAb-producing cell line A9 was selected as a partner for HRS-3 because of its efficiency in inducing lysis of the A9 hybridoma cells by resting N K cells. The hybrid hybridoma cell line HRS-3/A9 produced the supernatant with the strongest bispecific reactivity and was repeatedly subcloned and used for ascites production. Crude supernatant and purified HRS-3/A9 Bi-MAb triggered specific lysis of the CD30+ Hodgkin's-derived cell line L540, but not of the CD30cell line HPB-ALL by unstimulated peripheral-blood lymphocytes and NK-cell-enriched populations. Moreover, treatment of SClD mice bearing heterotransplanted human Hodgkin's tumors with HRS-3/A9 and human peripheral blood lymphocytes induced specific complete tumor regression in I O/ 10 animals. We thus report successful tumor treatment in an in vivo model using NK-cell-associated Bi-MAbs and show that the Bi-MAb HRS-3/A9 is an efficient promoter of the anti-tumor effects of NK cells in vitro and in vivo.