Immunological adjuvants are antigen non-specific substances, normally administered with the antigen, which enhance the specific immune response to that antigen. The only adjuvants currently in use for human vaccination are the mineral salts aluminum hydroxide and aluminum phosphate. The advances in vaccine technology mentioned above have therefore only served to heighten the need for new safe, effective immunological adjuvants. The search for new adjuvants covers a wide range of substances which differ both in chemical nature and in origin: bacterial, vegetable, or mineral. New approaches to vaccines have also led to research into new adjuvants of animal origin, as natural host molecules, including cytokines, have become available in large quantities as recombinant proteins. The cytokine system is a complex network of interactions, with cytokines exerting differing effects on different target cells, or on the same cells in different local environments, depending on the presence of other cytokines.