We have cross-linked, using succinimidyl 4-(N-maleimidomethyl) cyclohexane-1-carboxylate (SMCC) as a heterobifunctional reagent, anti-B16 melanoma monoclonal antibody to lymphokine activated killer (LAK) cells, independent of the Fc receptor. The conditions of such linkage were optimized so that the cytotoxic properties of LAK cells, as measured in a 4 h chromium release assay against fresh tumor cells, were preserved. Using the techniques described here, covalent cross linking of anti-B16 antibody to LAK cells preserved the reactivity of this antibody to antigens on B16 melanoma cells, and preserved the cytotoxic properties of the antibody-bound LAK cells to lyse B16 tumor cells and other tumor cells in vitro. Cross-linking antibody remained active on the surface of LAK cells for as long as 24h after the completion of binding. Treatment of established B16 melanoma pulmonary or subcutaneous (s.c.) tumors with LAK cells cross-linked to anti-B16 melanoma monoclonal antibody did not significantly alter their therapeutic efficacy over untreated cells. The possible explanations for these in vivo observations and suggested approaches to increase the efficacy of the cross-linked LAK cells are discussed.