Monoclonal antibodies (MoAb) to human melanoma have demonstrated a limited ability to cause tumor regression in humans when used alone or when coupled to gamma-emitting radioisotopes. We have evaluated heteroaggregates containing antilymphocyte antibodies crosslinked to antimelanoma monoclonal antibodies recognizing p97, a transferrin-like molecule (MoAb 96.5). When coupled to antibodies recognizing T3 (CD3, part of the T-cell receptor complex for antigen) or to 3G8, an antibody recognizing the Fc receptor present on large granular lymphocytes and granulocytes (CD16), significant induction of effector target crosslinks and target cell lysis could be obtained. Effector cells incubated for 24 hr with recombinant IL-2 were coated with the crosslinked reagents and tested for conjugate formation and for cytotoxicity in a 4-hr assay with chromium-labeled targets. Marked increases in conjugation to autologous tumor (47.0% compared to 11.8%) was demonstrated with E+ cells using the T3-coupled MoAb and with E- cells using the Fc receptor-coupled MoAb (22.6% compared to 11.2%). When tested in sequential cytotoxicity assays using unseparated effector cells incubated for 1, 2, and 3 days in IL-2, lytic activity was less than 2, less than 2, and 3.3 LU/10(6) cells for cells incubated in monomeric 96.5; 2.6, 5.3, and 50 LU/10(6) cells incubated in 96.5 crosslinked T3; and less than 2, 3.6, and 8.0 LU/10(6) cells for cells incubated with 96.5 crosslinked to 3G8. Similar findings were noted in two other experiments. Heteroaggregates such as these may be useful in conjunction with the transfer of IL-2-activated cells or with IL-2 alone in immunotherapy trials.