Although the initial rationale for the development of immunotherapy derived from the need to mobilize immune mechanisms in the treatment of cancer, it has become increasingly evident that immunotherapy has potential to benefit man in the treatment of a broad spectrum of disorders, including immunodeficiency, chronic infection, and autoimmunity. In embarking on such 'pro-host' forms of therapy, experimental therapists are leaving the traditional domains of pharmacology and entering the relatively undefined area of pharmacologic regulation of the immune system. In general, the application of immunotherapy has involved the administration of a bacterial product or a chemical to an animal or patient with an existing tumor or infection and the determination of changes in longevity or survival. The empiricism of this approach rests upon the assumption that the therapy is active on the immune response, in a favorable manner, under the conditions employed, and that the effect of the agent on the immune system will result in destruction of the tumor or the offending organism. The accumulated results of this approach are conflicting and have yielded mixed interpretations. A single unanimous interpretation is that more information about the function of the immune system and how to regulate it is required in order to mobilize it effectively in any particular disease state. There is, thus, the need for immunopharmacology --a basic, preclinical, and clinical science of therapeutic immune regulation.The purpose of this chapter will be to outline some of the basic areas of development of such a science and to summarize what is known about the cellular targets of immunotherapy and some of the intracellular mechanisms involved in the actions of various therapeutic agents. Of the diverse agents available, the crude bacterial preparations such as the mycobacteria (BCG), mixed bacterial vaccines, corynebacteria (C. parvum), and pseudomonas vaccine will not be discussed since their actions have been reviewed in this text and elsewhere; and since, as a result of their complex and antigenic nature, each preparation involves multiple mechanisms of action. From the ensuing discussion, it will become apparent that such bacterial preparations, when better defined as to their active constituents, will lend 0344-4325/79/0002/0035/$02.80