The administration of cytokines that augment the function of the immune system can be accomplished safely and without toxicity, provided a rational approach is used. Such a therapeutic method should be based upon the principles of pharmacology and the structure-activity relationships of the cytokine-receptor interaction. Thus, the therapeutic index should be determined, and the goal should be to augment the function of the immune system in a variety of clinical situations, not necessarily focused on eradicating a particular disease process such as metastatic cancer that may or may not be influenced by the immune system.