Cellular antimelanoma immune responses developed during the coincubation of spleen cells from naive C57BL/6 mice (H-2b) with LM mouse fibroblasts (H-2k) genetically modified to express melanoma-associated antigens (MAA) and to secrete interleukin (IL)-2 (RLBA-IL-2 cells). Antimelanoma responses also developed following coincubation of spleen cells from naive mice with allogeneic cells (H-2k) that expressed MAA, but did not secrete IL-2 (RLBA-ZipNeo cells), or allogeneic cells (H-2k) that secreted IL-2, but did not form MAA (LM-IL-2 cells). However, in these instances, the magnitude of the responses was significantly less (p<0.01) than followed coincubation of spleen cells with the allogeneic cell construct (RLBA-IL-2) that combined IL-2 secretion with the expression of MAA. LM(TK-) cells (H-2k) or B16 cells (H-2b) failed to generate antimelanoma immune responses in populations of spleen cells from C57BL/6 mice. The cell types involved in the induction of the antimelanoma response by the genetically modified cells were determined by prior depletion of T-cell subsets with monoclonal antibodies before the addition of the cellular immunogens. Antimelanoma responses failed to develop in spleen cell populations depleted of T-helper cells if the cellular immunogen was non-IL-2 secreting (RLBA-ZipNeo cells). Prior depletion of T-helper cells did not affect the induction of an antimelanoma response in cell populations coincubated with constructs (RLBA-IL-2 or LMIL- 2) modified to secrete IL-2. The role of macrophages in the induction of the antimelanoma response was indicated by failure of macrophage-depleted populations to develop responses following coincubation with IL-2-secreting or nonsecreting cell constructs.