The various immunologic parameters associated with melanoma bearing mice have been characterized. Information concerning the time of appearance, magnitude, and duration of free soluble antigen, antigen-antibody complexes, cytotoxic lymphoid cells, cytotoxic antibody, and non-cytotoxic antibody now make it possible to use this model system for evaluating the relative role of these factors in disease. Administration of lymphokines from human and murine cell lines to tumor bearing animals, and to in vivo and in vitro antibody synthesizing systems will permit an evaluation of the possible effect that these lymphoid cell products have on immunologic responses.