The various mechanisms by which four lymphokines (Macrophage Fusion Factor, Macrophage Mitogenic Factor, Migration Inhibitory Factor and Macrophage Aggregation Factor) alter the biological function(s) of alveolar and peritoneal macrophages shall be investigated by utilizing pharmacological active agents as a probe to dissect the various essential biological events leading to the altered cell activity. The pharmacological drugs can be broadly classified into 6 groups based on activity: (1) specific inhibition of lymphokine binding to membrane receptors; (2) specific alteration of cell membrane characteristics; (3) alteration of cyclic nucleotide levels; (4) alteration of cytoskeletal system; (5) specific inhibition of metabolic pathways; (6) agents with various activities. Macrophage Fusion Factor shall be characterized and purified by various methods including resistance to enzymes, stabilities and solubilities under various conditions and by several types of column chromatographies and isoelectric focusing. It shall be confirmed if the crude supernatants activate alveolar and/or peritoneal macrophages, if so, then whether the activity is tumoricidal or tumorstatic shall be determined. The specific lymphokine or lymphokine combinations responsible for macrophage activation shall be determined by the following experimental approaches: (1) Pharmacological; (2) Lymphokine purification; (3) Biological separation of lymphokines.