Recently we reported that cytotoxic T-cell clones can be retar eted to unrelated tumor cells by bispecific monoclonal antbodies (MAbs), anti-CDJ and anti-ovarian carcinoma (cuOCl TR) (Mezzanzanica eta/., 1988). In the perspective of in vivo tumor immunotherapy, as an alternative to cytotoxic T lymphocytes (CTL) from T-cell clones, since human peripheral blood mononuclear cells (PBMCs) without stimulation were quite ineffective, a suitable in vitro activation method was developed to render PBMCs lytic for relevant targets in the presence of the bispecific hybrid MAb cuOC/TR. This activation protocol was applied to PBMCs from 9 healthy donors (HD) and 6 ovarian carcinoma patients (P) and to tumorassociated lymphocytes (TAL) from 4 ovarian carcinoma P. The method consisted of in vitro stimulation with phytohemagglutinin (PHA) for 2 days, followed by culture with a low dose of recombinant human interleukin-2 (rlL-2) for 6 to 10 days. The antibody-mediated lysis of CTL from HD PBMCs was found to be specifically directed against cells expressing the relevant ovarian tumor antigen when different tumor cell lines and short-term cultures of tumor and normal cells were tested. The antibody-mediated lysis of CTL from P PBMCs or TAL was efficient both on autologous and allogeneic ovarian tumor cells, whereas no reactivity with autologous normal cells was observed and LAK activity was only evident in I out of 4 cases. The hybrid antibody induced cytotoxic activity of CTL from P was, however, lower than that of CTL from HD.