Since the landmark experiments of Ramon 60 years ago, attempts have been made to augment the humoral and cellular responses to administered antigens in order to develop more potent and less toxic vaccines. The need for an acceptable adjuvant suitable for clinical use has been underscored by recent advances in recombinant biotechnology and synthetic chemistry which have made it possible to create antigens that are smaller and better characterized, yet less immunogenic, than before. It is likely that these antigens will require an adjuvant to achieve protective immunity. Some of these same technological advances, together with a better understanding of the immune system in general, have permitted the study of adjuvants to evolve from an empirical field to a developmental one. This article discusses the currently known agents capable of immunopotentiation and possible strategies for their use in future vaccines.